INVESTOR RIGHTS AGREEMENT

Exhibit 4.1

INVESTOR RIGHTS AGREEMENT

     THIS INVESTOR RIGHTS AGREEMENT (the “ Agreement ”) is entered into as of June 2, 2008, by and among MarketAxess Holdings Inc., a Delaware corporation (including its successors and permitted assigns, the “ Company ”), TCV VI, L.P., a Delaware limited partnership (“ TCV VI ”), and TCV Member Fund, L.P., a Delaware limited partnership (“ TCV Member Fund ” and, together with TCV VI, the “ Investors ”). Capitalized terms used but not defined elsewhere herein are defined in Section 1.

RECITALS

     1. The Company has entered into a Securities Purchase Agreement, dated as of the date hereof (as amended from time to time, the “ Purchase Agreement ”), with each of the Investors pursuant to which the Company has sold to the Investors, and the Investors have purchased from the Company, (i) an aggregate of 35,000 shares of the Series B Preferred Stock, which is convertible into shares of the Company’s voting common stock, par value $0.003 per share (“ Common Stock ”), and (ii) warrants to purchase an aggregate of 700,000 shares of Common Stock (the “ Warrants ”).

     2. As a condition to each of the Investors’ obligations under the Purchase Agreement, the Company and the Investors will enter into this Agreement for the purpose of granting certain registration and other rights to the Investors, as well as imposing certain restrictions on the ability of the Investors to Transfer their Securities and engage in certain other activities.

     NOW, THEREFORE, in consideration of the covenants and promises set forth herein, and for other good and valuable consideration, intending to be legally bound hereby the parties agree as follows:

     SECTION 1. Certain Definitions . As used in this Agreement, the capitalized terms identified in the Preamble and the Recitals shall have the meanings identified therein and the following terms shall have the following respective meanings:

          “ Agreement ” shall have the meaning set forth in the Preamble hereof.

          “ Commission ” shall mean the Securities and Exchange Commission or any other federal agency at the time administering the Securities Act or the Exchange Act.

          “ Common Stock ” shall have the meaning set forth in the Recitals hereof.

          “ Company ” shall have the meaning set forth in the Preamble hereof.

          “ Company Indemnified Parties ” shall have the meaning set forth in Section 10(a) hereof.

          “ Competitor ” means any of the persons set forth on Exhibit A attached hereto.

          “ Effectiveness Period ” shall have the meaning set forth in Section 5(b) hereof.

          “ Exchange Act ” shall mean the Securities Exchange Act of 1934, as amended, or any similar successor federal statute, and the rules and regulations of the Commission thereunder, all as the same shall be in effect from time to time.

          “ Holder ” shall mean (i) any Investor holding Registrable Securities and (ii) any member of general or limited partner of an Investor or other person to whom the rights under this Agreement have been transferred in accordance with Section 13 hereof.

          “ Holder Indemnified Parties ” shall have the meaning set forth in Section 10(b) hereof.

          “ Indemnified Party ” shall have the meaning set forth in Section 10(c) hereof.

          “ Indemnifying Party ” shall have the meaning set forth in Section 10(c) hereof.

          “ Investors ” shall have the meaning set forth in the Preamble hereof.

          “ Lockup Period ” shall have the meaning set forth in Section 2 hereof.

          “ person ” means an individual, corporation, partnership, limited liability company, joint venture, association, trust, unincorporated organization, other legal entity, or any government or governmental agency or authority.

          “ Purchase Agreement ” shall have the meaning set forth in the Recitals hereof.

          “ register ,” “ registered ” and “ registration ” refer to a registration effected by preparing and filing a registration statement in compliance with the Securities Act, and the declaration or ordering of the effectiveness of such registration statement.

          “ Registration Expenses ” shall mean all expenses incurred by the Company in complying with Sections 5 and 6 hereof, including, without limitation, all registration, qualification, listing and filing fees, printing expenses, escrow fees, fees and disbursements of counsel for the Company, blue sky fees and expenses, and the expense of any special audits incident to or required by any such registration, provided , however , that Registration Expenses shall not be deemed to include any Selling Expenses.

          “ Registrable Securities ” shall mean (i) any shares of Common Stock paid as a dividend on any shares of Series B Preferred Stock or issuable upon conversion of any share of Series B Preferred Stock, (ii) any shares of Common Stock issuable upon exercise of the Warrants, and (iii) any Common Stock or other securities issued or issuable in respect of the securities described in clauses (i) and (ii) above, or this clause (iii) upon any stock split, stock dividend, recapitalization, reclassification, merger, consolidation or similar event; provided, however , that such securities shall only be treated as Registrable Securities until the earliest of: (w) the date on which such security has been registered under the Securities Act and disposed of in accordance with an effective Registration Statement relating thereto; (x) the date on which such security has been sold pursuant to Rule 144 and the security is no longer a Restricted

Security; (y) the date on which all Registrable Securities owned by the Holder thereof may be resold without volume or other restrictions during any and all three-month periods pursuant to Rule 144; or (z) the date on which such security is transferred in a transaction pursuant to which the registration rights are not also assigned in accordance with Section 13 hereof.

          “ Resale Shelf Registration ” shall have the meaning set forth in Section 5(a) hereof.

          “ Restricted Affiliate ” means: (a) any person who is directly or indirectly responsible for the formation, management, operations, oversight or administration of the Purchasers (including, without limitation, any principals, partners or employees of any such person); and (b) any investment fund directly or indirectly formed, managed or controlled by any one or more persons referred to in the preceding clause (a).

          “ Restricted Securities ” shall mean the Securities required to bear the first legend set forth in Section 3 hereof.

          “ Rule 144 ” shall mean Rule 144 promulgated under the Securities Act and any successor provision.

          “ Securities ” shall mean all shares of Series B Preferred Stock purchased by the Investors pursuant to the Purchase Agreement, all shares of Series B Preferred Stock issued to the Investors as dividends, the Warrants, all shares of Common Stock issuable upon conversion of the Series B Preferred Stock or upon exercise of the Warrants and all shares of Common Stock issued or issuable in respect of any of the foregoing.

          “ Securities Act ” shall mean the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder or any similar federal statute and the rules and regulations of the Commission thereunder, all as the same shall be in effect at the time.

          “ Selling Expenses ” shall mean all underwriting discounts, selling commissions and stock transfer taxes applicable to the securities registered by the Holders.

          “ Series B Preferred Stock ” shall mean the Company’s Series B Preferred Stock, par value $0.001 per share.

          “ Shelf Registration ” shall mean the Resale Shelf Registration or a Subsequent Shelf Registration, as applicable.

          “ Subsequent Holder Notice ” shall have the meaning set forth in Section 5(e) hereof.

          “ Subsequent Shelf Registration ” shall have the meaning set forth in Section 5(c) hereof.

          “ TCV VI ” shall have the meaning set forth in the Preamble hereof.

          “ TCV Member Fund ” shall have the meaning set forth in the Preamble hereof.

          “ Transfer ” shall mean any, direct or indirect, pledge, sale, contract to sell, assignment, transfer or other encumbrance or disposition.

          “ Underwritten Offering ” shall have the meaning set forth in Section 5(f) hereof.

          “ Underwritten Offering Notice ” shall have the meaning set forth in Section 5(f) hereof.

          “ Warrants ” shall have the meaning set forth in the Recitals hereof.

     SECTION 2. Transfer Restrictions .

     (a) From the date hereof until the first anniversary of this Agreement (such period being the “ Lockup Period ”) the Investors shall not Transfer any Securities without the prior written consent of the Company; provided , that in the event the Board of Directors shall (i) approve a tender offer for a majority of the outstanding capital stock of the Company or (ii) approve a merger or consolidation of the Company with any other person that would result in the voting securities of the Company outstanding immediately prior thereto representing less than a majority of the voting power to elect a majority of the board of directors or similar body of the person surviving such merger or resulting from such consolidation, then the Investors shall be permitted to tender shares of Common Stock into such tender offer or deliver shares of Common Stock in connection with the consummation of such merger.

     (b) At no time, without the prior written consent of the Company, will the Investors Transfer (i) any of the Series B Preferred Stock or Warrants to any Competitor or (ii) any of the Common Stock issuable upon conversion of the Series B Preferred Stock or upon exercise of the Warrants to any Competitor in a privately negotiated transaction. The Investors will not knowingly participate in a series of privately negotiated transactions which results in the Transfer of any Securities to any Competitor. In addition, no shares of Series B Preferred Stock or Warrants may be Transferred, unless the Transferee agrees to be bound by the terms of this Section 2(b).

     (c) In any event, Restricted Securities shall not be Transferred except upon the conditions specified in Section 4, which conditions are intended to ensure compliance with the provisions of the Securities Act. Any attempted Transfer in violation of this Section 2 shall be void ab initio .

     SECTION 3. Restrictive Legend . Each certificate representing the Securities (unless otherwise permitted by the provisions of Section 4 below) shall be stamped or otherwise imprinted with a legend in the following form (in addition to any legend required under applicable state securities laws):

“THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR

DISTRIBUTION THEREOF. SUCH SHARES MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT THEREUNDER OR AN EXEMPTION FROM SUCH REGISTRATION.”

          In addition, for so long as the Securities are subject to the restrictions set forth in Section 2, each certificate representing the Securities shall be stamped or otherwise imprinted with a legend in the following form:

“THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS ON TRANSFER SET FORTH IN AN INVESTOR RIGHTS AGREEMENT. THE COMPANY WILL MAIL TO THE HOLDER OF THIS CERTIFICATE A COPY OF SUCH INVESTOR RIGHTS AGREEMENT, AS IN EFFECT ON THE DATE OF MAILING, WITHOUT CHARGE, PROMPTLY AFTER RECEIPT OF A WRITTEN REQUEST THEREFOR.”

          Each Investor consents to the Company making a notation on its records and giving instructions to any transfer agent of the Restricted Securities in order to implement the restrictions on transfer set forth in Section 2.

     SECTION 4. Notice of Proposed Transfers . Each Holder shall comply in all respects with the provisions of this Section 4. Prior to any proposed Transfer of any Restricted Securities, unless there is in effect a registration statement under the Securities Act covering the proposed Transfer, a Holder shall give written notice to the Company of such Holder’s intention to effect such Transfer. Each such notice shall describe the manner and circumstances of the proposed Transfer in sufficient detail, and shall be accompanied by either (a) an opinion of legal counsel reasonably satisfactory to the Company to the effect that the proposed Transfer of the Restricted Securities may be effected without registration under the Securities Act, (b) a “no action” letter from the Commission to the effect that the Transfer of such securities without registration will not result in a recommendation by the staff of the Commission that action be taken with respect thereto or (c) any other evidence reasonably satisfactory to counsel to the Company, whereupon such Investor shall be entitled to Transfer such Restricted Securities in accordance with the terms of the notice delivered by such Investor to the Company. Notwithstanding the foregoing, in the event a Holder shall give the Company a representation letter containing such representations as the Company shall reasonably request, the Company will not require such a notice or legal opinion or “no action” letter or such other evidence (x) in any transaction in compliance with Rule 144, (y) in any transaction in which a Holder that is a corporation distributes Restricted Securities solely to its majority owned subsidiaries or Affiliates for no consideration or (z) in any transaction in which a Holder that is a partnership or limited liability company distributes Restricted Securities solely to its Affiliates (including affiliated fund partnerships), or partners or members of such Holder or its Affiliates for no consideration (and to the extent the Securities will be Restricted Securities when held by such transferees they agree to be bound by the terms of this Agreement). Each certificate evidencing the Restricted Securities transferred shall bear the appropriate restrictive legend set forth in Section 3 above, except that such certificate shall not bear the first such restrictive legend if such legend is not required in order to establish compliance with any provisions of the Securities Act. Upon the request of a Holder of a

certificate bearing the first such restrictive legend and, if necessary, the appropriate evidence as required by clause (a), (b) or (c) of the third sentence of this Section 4, the Company shall remove the first such restrictive legend from such certificate and from the certificate to be issued to the applicable transferee if such legend is not required in order to establish compliance with any provisions of the Securities Act and the Holder promptly Transfers the Security. Upon the request of a Holder of a certificate bearing the second restrictive legend, the Company shall remove such restrictive legend from such certificate when the provisions of Section 2 are no longer applicable to such Security.

     SECTION 5. Resale Shelf Registration .

          (a) The Company shall use its best efforts to file within six months of the date hereof a registration statement covering the sale or distribution from time to time by the Holders, on a delayed or continuous basis pursuant to Rule 415 of the Securities Act, including without limitation, by way of underwritten offering, block sale or other distribution plan designated by the Holders of a majority of the Registrable Securities, of all of the Registrable Securities on Form S-3 (except if the Company is not then eligible to register for resale the Registrable Securities on Form S-3, then such registration shall be on another appropriate form and shall provide for the registration of such Registrable Securities for resale by such Holders in accordance with any reasonable method of distribution elected by the Holders) (the “ Resale Shelf Registration Statement ”) and shall use its best efforts to cause such Resale Shelf Registration to be declared effective by the Commission as promptly as possible after the filing thereof, but in any event prior to the twelve month anniversary of the date of this Agreement.

          (b) Once declared effective, the Company shall, subject to Section 9(j), use its best efforts to cause the Resale Shelf Registration to be continuously effective and usable until such time as there are no longer any Registrable Securities (the “ Effectiveness Period ”).

          (c) If any Shelf Registration ceases to be effective under the Securities Act for any reason at any time during the Effectiveness Period, the Company shall use its commercially reasonable efforts to promptly cause such Shelf Registration to again become effective under the Securities Act (including obtaining the prompt withdrawal of any order suspending the effectiveness of such Shelf Registration), and in any event shall within 30 days of such cessation of effectiveness, amend such Shelf Registration in a manner reasonably expected to obtain the withdrawal of any order suspending the effectiveness of such Shelf Registration or, file an additional registration statement (a “ Subsequent Shelf Registration ”) for an offering to be made on a delayed or continuous basis pursuant to Rule 415 of the Securities Act registering the resale from time to time by Holders thereof of all securities that are Registrable Securities as of the time of such filing. If a Subsequent Shelf Registration is filed, the Company shall use its commercially reasonable efforts to (x) cause such Subsequent Shelf Registration to become effective under the Securities Act as promptly as is reasonably practicable after such filing, but in no event later than the date that is 90 days after such Subsequent Shelf Registration is filed and (y) keep such Subsequent Shelf Registration (or another Subsequent Shelf Registration) continuously effective until the end of the Effectiveness Period. Any such Subsequent Shelf Registration shall be a Registration Statement on Form S-3 to the extent that the Company is eligible to use such form. Otherwise, such Subsequent Shelf Registration shall be on another

appropriate form and shall provide for the registration of such Registrable Securities for resale by such Holders in accordance with any reasonable method of distribution elected by the Holders.

          (d) The Company shall supplement and amend any Shelf Registration if required by the rules, regulations or instructions applicable to the registration form used by the Company for such Shelf Registration if required by the Securities Act or as reasonably requested by the Holders covered by such Shelf Registration.

          (e) If a person becomes a Holder of Registrable Securities after a Shelf Registration becomes effective under the Securities Act, the Company shall, as promptly as is reasonably practicable following delivery of written notice to the Company of such person becoming a Holder and requesting for its name to be included as a selling securityholder in the prospectus related to the Shelf Registration (a “ Subsequent Holder Notice ”), and in any event within 15 days after such date:

               (i) if required and permitted by applicable law, file with the Commission a supplement to the related prospectus or a post-effective amendment to the Shelf Registration and any necessary supplement or amendment to any document incorporated therein by reference and file any other required document with the Commission so that such Holder is named as a selling securityholder in the Shelf Registration and the related prospectus in such a manner as to permit such Holder to deliver a prospectus to purchasers of the Registrable Securities in accordance with applicable law; provided , however , that if a post-effective amendment is required by the rules and regulations of the Commission in order to permit resales by such Holder, the Company shall not be required to file more than one post-effective amendment or a supplement to the related prospectus for such purpose in any 45-day period;

               (ii) if, pursuant to Section 5(e)(i), the Company shall have filed a post-effective amendment to the Shelf Registration, use its efforts to cause such post-effective amendment to become effective under the Securities Act as promptly as is reasonably practicable, but in any event by the date that is 60 days after the date such post-effective amendment is required by this Section 5(e) to be filed; and

               (iii) notify such Holder as promptly as is reasonably practicable after the effectiveness under the Securities Act of any post-effective amendment filed pursuant to clause (i) above.

          (f) The Holders of a majority of the Registrable Securities may on one occasion after the Resale Shelf Registration Statement becomes effective deliver a written notice to the Company (the “ Underwritten Offering Notice ”) specifying that the sale of some or all of the Registrable Securities subject to the Shelf Registration, not to be less than 1,000,000 shares of Registrable Securities, is intended to be conducted through an underwritten offering (the “ ›Underwritten Offering ”). In the event of an Underwritten Offering:

               (i) The Holders of a majority of Registrable Securities to be included in such Underwritten Offering shall have the right to select the managing underwriter or underwriters to administer the offering; provided , however, that such managing underwriter or underwriters shall be reasonably acceptable to the Company.

               (ii) The Holders of Registrable Securities to be included in such Underwritten Offering and the Company shall enter into an underwriting agreement in such customary form as shall have been negotiated and agreed to by the Company with the underwriter or underwriters selected for such underwriting.

               (iii) Notwithstanding any other provision of this Section 5, if the managing underwriter or underwriters of a proposed Underwritten Offering advises the Board of Directors of the Company that in its or their opinion the number of Registrable Securities requested to be included in such Underwritten Offering exceeds the number which can be sold in such Underwritten Offering in light of market conditions, the Registrable Securities shall be included on a pro rata basis upon the number of securities that each Holder shall have requested to be included in such offering. To facilitate the allocation of shares in accordance with the above provisions, the Company or the managing underwriters may round the number of shares allocated to any Holder or other holder to the nearest 100 shares. If any Holder disapproves of the terms of any such underwriting, such Holder may elect to withdraw therefrom by written notice to the Company and the managing underwriter or underwriters.

          (g) In the event any Holder requests to participate in a Shelf Registration pursuant to this Section 5 in connection with a distribution of Registrable Securities to its partners or members, the Shelf Registration shall in the event such distribution and subsequent resale is permitted by applicable law provide for resale by such partners or members, if requested by such Holder.

     SECTION 6. Company Registration .

          (a)  Notice of Registration . If at any time or from time to time the Company shall determine to file a registration statement for an underwritten public offering of its equity securities (for the avoidance of doubt, the following will not apply to any registration statement filed on a Form S-4, Form S-8 or any successor forms), the Company will:

               (i) promptly give to each Holder written notice thereof; and

               (ii) subject to Section 6(b) below, include in such registration and underwritten offering (and any related qualification under blue sky laws or other compliance) all the Registrable Securities specified in a written request or requests made within 10 days after receipt of such written notice from the Company by any Holder.

          (b)  Underwriting . The right of any Holder to registration pursuant to this Section 6 shall be conditioned upon such Holder’s participation in such underwriting and the inclusion of Registrable Securities in the underwriting to the extent provided herein. Each Holder proposing to distribute its securities through such underwriting shall (together with the Company and the other holders distributing their securities through such underwriting) enter into and perform such Holder’s obligations under an underwriting agreement with the managing underwri