MIAMI INTERNATIONAL HOLDINGS, INC.

As filed with the U.S. Securities and Exchange Commission on December 9, 2025

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORMS-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

(Exact name of registrant as specified in its charter)

7 Roszel Road, Suite 1A

Princeton, NJ 08540

(609)897-7300

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Thomas P. Gallagher

Chairman and Chief Executive Officer

7 Roszel Road, Suite 1A

Princeton, New Jersey 08540

(609) 897-7300

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Approximate date of commencement of proposed sale to the public: As soon as practicable after this Registration Statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended, check the following box.☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.☒

The registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

PRELIMINARY PROSPECTUS (Subject to Completion)

Dated December 9, 2025

6,750,000 Shares

This prospectus relates to the offer and sale by the selling stockholders identified in this prospectus of up to an aggregate of 6,750,000 shares of our common stock, par value $0.001 per share.

We are not selling any shares of common stock under this prospectus, and we will not receive any of the proceeds from the sale of shares of our common stock by the selling stockholders. The selling stockholders will bear all commissions and discounts attributable to their respective sales of the securities.

Our shares of common stock are listed on the New York Stock Exchange (“NYSE”) under the symbol “MIAX”. On December 8, 2025, the closing price of our common stock was $45.56 per share.

Our amended and restated certificate of incorporation contains certain voting and ownership limitations and transfer restrictions that will remain in place for as long as we control a registered U.S. national securities exchange. Specifically, our amended and restated certificate of incorporation prohibits (i) any person from owning greater than 40% of any class of our capital stock, (ii) exchange members from owning greater than 20% of any class of our capital stock and (iii) all persons from voting shares representing more than 20% of the voting power of our then issued and outstanding capital stock either alone or together with any related persons, in each case subject to certain conditions and exceptions, including the waiver by the board of directors (except with respect to exchange members). There are also certain other regulatory limitations on the ownership and transfer of our capital stock. See the section titled “Description of Capital Stock.”

We are an “emerging growth company” under the federal securities laws and, as such, have elected to comply with certain reduced public company reporting requirements for this prospectus and future filings. See the section titled “Prospectus Summary — Implications of Being an Emerging Growth Company.”

Investing in our common stock involves risks. See the section titled “Risk Factors” beginning on page 25 of this prospectus to read about factors you should consider before deciding to invest in shares of our common stock.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

(1)See the section titled “Underwriting (Conflicts of Interest)” for a description of the compensation payable to the underwriters.

The selling stockholders have granted the underwriters an option for a period of 30 days to purchase up to 1,012,500 additional shares of our common stock at the public offering price less the underwriting discounts and commissions.

The underwriters expect to deliver the shares against payment in New York, New York on , 2025.

Lead Joint Bookrunning Managers

Joint Bookrunning Managers

, 2025

TABLE OF CONTENTS

You should rely only on the information contained in this prospectus, any amendment or supplement to this prospectus or any free writing prospectus that we may authorize to be delivered or made available to you. Neither we, the selling stockholders nor the underwriters have authorized anyone to provide any information or to make any representations other than those contained in this prospectus, any amendment or supplement to this prospectus or any free writing prospectuses prepared by us or on our behalf. Neither we, the selling stockholders nor the underwriters take any responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus, any amendment or supplement to this prospectus or any applicable free writing prospectus is an offer to sell only the shares offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. The information contained in this prospectus, any amendment or supplement to this prospectus or any applicable free writing prospectus is current only as of its date, regardless of the time of delivery of this prospectus, any amendment or supplement to this prospectus or any applicable free writing prospectus or any sale of the shares. Our business, financial condition, results of operations and prospects may have changed since such date.

Trademarks

We own MIAX®, MIAX Options®, MIAX Pearl®, MIAX Emerald® and MIAX Sapphire® as trademarks or service marks in the United States and certain other jurisdictions. MIAX Futures™ and TINI™ are currently pending.

This prospectus contains references to our trademarks and service marks and to those belonging to other entities. Solely for convenience, trademarks and trade names referred to in this prospectus, including logos, artwork, and other visual displays, may appear without the® or ™ symbols, but in the case of our trademarks and trade names or those of our licensors, such references are not intended to indicate in any way that we will not assert, to the fullest

i extent under applicable law, our rights or the rights of the applicable licensor to these trademarks and trade names. We do not intend our use or display of other entities’ trade names, trademarks, or service marks to imply a relationship with, or endorsement or sponsorship of us by, any other entity.

ii