# EDGAR Filing Document

**Accession Number:** 0001438472
**File Stem:** 0001628280-25-056735
**Filing Date:** 2025-12
**Character Count:** 28336
**Document Hash:** ebaf76ede3e4b835e1451e5801adf79c
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001628280-25-056735.hdr.sgml**: 20251212

**ACCESSION NUMBER**: 0001628280-25-056735

**CONFORMED SUBMISSION TYPE**: POS AM

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20251212

**DATE AS OF CHANGE**: 20251212

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** MIAMI INTERNATIONAL HOLDINGS, INC.
- **CENTRAL INDEX KEY:** 0001438472
- **STANDARD INDUSTRIAL CLASSIFICATION:** SECURITY BROKERS, DEALERS & FLOTATION COMPANIES [6211]
- **ORGANIZATION NAME:** 09 Crypto Assets
- **EIN:** 261482385
- **STATE OF INCORPORATION:** DE

**FILING VALUES:**
- **FORM TYPE:** POS AM
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-292028
- **FILM NUMBER:** 251567907

**BUSINESS ADDRESS:**
- **STREET 1:** 7 ROSZEL ROAD
- **STREET 2:** FIFTH FLOOR, SUITE 1-A
- **CITY:** PRINCETON
- **STATE:** NJ
- **ZIP:** 08540
- **BUSINESS PHONE:** 609-897-7300

**MAIL ADDRESS:**
- **STREET 1:** 7 ROSZEL ROAD
- **STREET 2:** FIFTH FLOOR, SUITE 1-A
- **CITY:** PRINCETON
- **STATE:** NJ
- **ZIP:** 08540

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** MIAMI INTERNATIONAL HOLDINGS INC
- **DATE OF NAME CHANGE:** 20080624

**As filed with the U.S. Securities and Exchange Commission on December 12, 2025**

**Registration No. 333-292028** 

**UNITED STATES**

**SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

**Post-Effective Amendment No. 1**

**to**

**FORM S-1**

**REGISTRATION STATEMENT**

**UNDER**

**THE SECURITIES ACT OF 1933**

**Miami International Holdings, Inc.**

(Exact name of registrant as specified in its charter)

---

| | | |
|:---|:---|:---|
| **Delaware** | **6200** | **26-1482385** |
| (State or other jurisdiction of incorporation or organization) | (Primary Standard Industrial Classification Code Number) | (I.R.S. Employer Identification No.) |

---

**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**

**Miami International Holdings, Inc.**

**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)

---

| | | |
|:---|:---|:---|
| ***Copies to:*** | ***Copies to:*** | ***Copies to:*** |
| **Herbert F. Kozlov, Esq.**<br>**Danielle Carbone, Esq.**<br>**Reed Smith LLP**<br>**599 Lexington Avenue**<br>**New York, New York 10022**<br>**(212) 521-5400** | **Barbara Comly, Esq.<br>Executive Vice President, General<br>Counsel and Corporate Secretary<br>Miami International Holdings, Inc.<br>7 Roszel Road, Suite 1A<br>Princeton, New Jersey 08540<br>(609) 897-7300** | **Paul Tropp, Esq.**<br>**Ropes & Gray LLP**<br>**1211 Avenue of the Americas**<br>**New York, New York 10036**<br>**(212) 569-9000** |

---

**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. ☒ 333-292028

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.

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| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ☐ | Accelerated filer | ☐ |
| Non-accelerated filer | ☒ | Smaller reporting company | ☐ |
| | | Emerging growth company | ☒ |

---

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.**

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**EXPLANATORY NOTE**

Miami International Holdings, Inc., a Delaware corporation (the "Company"), filed a Registration Statement on Form S-1 on December 9, 2025 (333-292028), which was declared effective on December 11, 2025, (the "Registration Statement"). This Post-Effective Amendment No. 1 to the Registration Statement on Form S-1 (the "Post-Effective Amendment") is being filed solely to correct typographical errors in Exhibit 5.1. No other changes have been made to the Registration Statement.

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**PART II**

**INFORMATION NOT REQUIRED IN PROSPECTUS**

**Item 16. Exhibits and Consolidated Financial Statement Schedules.**

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;***(a)Exhibits***

See the Exhibit Index included in this Registration Statement, which is incorporated by reference herein.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;***(b)Consolidated Financial Statement Schedules***

Schedules not listed above have been omitted because the information required to be set forth therein is not applicable or is shown in the consolidated financial statements or interim condensed consolidated financial statements or notes thereto.

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**EXHIBIT INDEX**

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| | |
|:---|:---|
| **Exhibit Number** | **Exhibit Description** |
| 1.1 | <u>[Form of Underwriting Agreement (Incorporated by reference to Exhibit 1.1 to the Company's Registration Statement on Form S-1 (333-292028) filed with the SEC on December 9, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/exhibit11-sx1december2025.htm)</u> |
| 3.1 | <u>[Amended and Restated Certificate of Incorporation of the Registrant (Incorporated by reference to Exhibit 3.1 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit31-sx1.htm)</u> |
| 3.2 | <u>[Amended and Restated By-Laws of the Registrant (Incorporated by reference to Exhibit 3.2 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit32-sx1.htm)</u> |
| 4.1 | <u>[Form of Voting Common Stock Certificate (Incorporated by reference to Exhibit 4.1 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit41-sx1.htm)</u> |
| 4.2≠ | <u>[Warrant Issued to FCS Advisors LLC, d/b/a Brevet Capital Advisors dated July 29, 2021 for 200,000 shares (Incorporated by reference to Exhibit 4.2 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit42-sx1.htm)</u> |
| 4.3≠ | <u>[Warrant Issued to FCS Advisors LLC, d/b/a Brevet Capital Advisors dated December 4, 2023 for 200,000 shares (Incorporated by reference to Exhibit 4.3 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit43-sx1.htm)</u> |
| 4.4≠ | <u>[Warrant Issued to Skylight Aggregator, L.P. dated November 4, 2024 for 2,800,291 shares (Incorporated by reference to Exhibit 4.4 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit44-sx1.htm)</u> |
| 4.5≠ | <u>[Warrant Issued to Skylight Aggregator, L.P. dated November 4, 2024 for 4,200,436 shares (Incorporated by reference to Exhibit 4.5 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit45-sx1.htm)</u> |
| 4.6≠ | <u>[Warrant Issued to WPCS FF Excelsior, L.P. dated November 4, 2024 for 354,240 shares (Incorporated by reference to Exhibit 4.6 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit46-sx1.htm)</u> |
| 4.7≠ | <u>[Warrant Issued to WPCS FF Excelsior, L.P. dated November 4, 2024 for 236,160 shares (Incorporated by reference to Exhibit 4.7 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit47-sx1.htm)</u> |
| 4.8≠ | <u>[Warrant Issued to Citadel Securities Principal Investments LLC. dated June 30, 2025 for 12,437,007 shares (Incorporated by reference to Exhibit 4.8 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit48-sx1.htm)</u> |
| 5.1\* | <u>[Opinion of Gallagher, Briody & Butler](exhibit51-posam.htm)</u> |
| 10.1+ | <u>[Miami International Holdings, Inc. 2008 Stock Incentive Plan, as amended (Incorporated by reference to Exhibit 10.1 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit101-sx1.htm)</u> |
| 10.2+ | <u>[Miami International Holdings, Inc. 2008 Stock Incentive Plan for Non-Employee Directors and Members of the Board of Advisors, as amended (Incorporated by reference to Exhibit 10.2 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit102-sx1.htm)</u> |
| 10.3+ | <u>[Form of Miami International Holdings, Inc. Stock Option Agreement \[for Employees\] pursuant to 2008 Stock Incentive Plan, as amended (Incorporated by reference to Exhibit 10.3 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit103-sx1.htm)</u> |
| 10.4+ | <u>[Form of Miami International Holdings, Inc. Non-Qualified Stock Option Agreement \[for Non-Employee Directors\] pursuant to 2008 Stock Incentive Plan for Non-Employee Directors and Members of the Board of Advisors, as amended (Incorporated by reference to Exhibit 10.4 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit104-sx1.htm)</u> |
| 10.5+ | <u>[Miami International Holdings, Inc. 2013 Stock Option and Incentive Plan for Employees and Consultants, as amended (Incorporated by reference to Exhibit 10.5 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit105-sx1.htm)</u> |

---

------

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| | |
|:---|:---|
| **Exhibit Number** | **Exhibit Description** |
| 10.6+ | <u>[Miami International Holdings, Inc. 2013 Stock Option and Incentive Plan for Non-Employee Directors, Committee Members and Members of the Board of Advisors, as amended (Incorporated by reference to Exhibit 10.6 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit106-sx1.htm)</u> |
| 10.7+ | <u>[Form of Miami International Holdings, Inc. Notice of Stock Option Grant and Stock Option Award Agreement pursuant to 2013 Stock Option and Incentive Plan for Employees and Consultants, as amended (Incorporated by reference to Exhibit 10.7 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit107-sx1a.htm)</u> |
| 10.8+ | <u>[Form of Miami International Holdings, Inc. Restricted Stock Award Agreement pursuant to 2013 Stock Option and Incentive Plan for Employees and Consultants, as amended (Incorporated by reference to Exhibit 10.8 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit108-sx1.htm)</u> |
| 10.9+ | <u>[Form of Miami International Holdings, Inc. Notice of Stock Option Grant and Stock Option Award Agreement pursuant to 2013 Stock Option and Incentive Plan for Non-Employee Directors, Committee Members and Members of the Board of Advisors, as amended (Incorporated by reference to Exhibit 10.9 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit109-sx1.htm)</u> |
| 10.10+ | <u>[Miami International Holdings, Inc. 2021 Stock Option and Incentive Plan for Employees and Consultants (Incorporated by reference to Exhibit 10.10 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1010-sx1.htm)</u> |
| 10.11+ | <u>[Form of Miami International Holdings, Inc. Notice of Stock Option Grant and Stock Option Award Agreement pursuant to 2021 Stock Option and Incentive Plan for Employees and Consultants (Incorporated by reference to Exhibit 10.11 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1011-sx1.htm)</u> |
| 10.12+ | <u>[Form of Miami International Holdings, Inc. Restricted Stock Award Agreement pursuant to 2021 Stock Option and Incentive Plan for Employees and Consultants (Incorporated by reference to Exhibit 10.12 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1012-sx1.htm)</u> |
| 10.13+ | <u>[Omnibus Amendment to Stock Incentive Plans of Miami International Holdings, Inc. (Incorporated by reference to Exhibit 10.13 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1013-sx1.htm)</u> |
| 10.14+ | <u>[Miami International Holdings, Inc. 2022 Equity Incentive Plan (Incorporated by reference to Exhibit 10.14 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1014-sx1.htm)</u> |
| 10.15+ | <u>[Form of Notice of Stock Option Grant and Stock Option Award Agreement pursuant to the Miami International Holdings, Inc. 2022 Equity Incentive Plan (Incorporated by reference to Exhibit 10.15 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1015-sx1.htm)</u> |
| 10.16+ | <u>[Form of Restricted Stock Award Agreement pursuant to the Miami International Holdings, Inc. 2022 Equity Incentive Plan (Incorporated by reference to Exhibit 10.16 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1016-sx1.htm)</u> |
| 10.17+ | <u>[Miami International Holdings, Inc. Transaction Incentive Plan (Incorporated by reference to Exhibit 10.17 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1017-sx1.htm)</u> |
| 10.18+ | <u>[Form of Award Agreement pursuant to Miami International Holdings, Inc. Transaction Incentive Plan (Incorporated by reference to Exhibit 10.18 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1018-sx1.htm)</u> |
| 10.19 | <u>[Form of Indemnification Agreement (Incorporated by reference to Exhibit 10.19 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1019-sx1.htm)</u> |

---

------

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| | |
|:---|:---|
| **Exhibit Number** | **Exhibit Description** |
| 10.20+# | <u>[Amended and Restated Employment Agreement effective as of January 1, 2024 by and between Miami International Holdings, Inc. and Shelly Brown (Incorporated by reference to Exhibit 10.20 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1020-sx1.htm)</u> |
| 10.21+≠ | <u>[Amended and Restated Employment Agreement dated as of July 17, 2025 between Miami International Holdings, Inc. and Thomas P. Gallagher (Incorporated by reference to Exhibit 10.21 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1021-sx1.htm)</u> |
| 10.22+# | <u>[Amended and Restated Employment Agreement dated July 1, 2024 by and between Miami International Holdings, Inc. and Douglas M. Schafer Jr. (Incorporated by reference to Exhibit 10.22 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1022-sx1.htm)</u> |
| 10.23≠# | <u>[Exchange Agreement by and among Miami International Holdings, Inc. and Citadel Securities Principal Investments LLC, dated as of June 30, 2025 (Incorporated by reference to Exhibit 10.24 to the Company's Registration Statement on Form S-1 (333-288767) filed with the SEC on July 18, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025035343/exhibit1024-sx1.htm)</u> |
| 21.1 | <u>[List of Subsidiaries of the Registrant (Incorporated by reference to Exhibit 21.1 to the Company's Registration Statement on Form S-1 (333-292028) filed with the SEC on December 9, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/exhibit211-sx1december2025.htm)</u> |
| 23.1 | <u>[Consent of KPMG LLP (Incorporated by reference to Exhibit 23.1 to the Company's Registration Statement on Form S-1 (333-292028) filed with the SEC on December 9, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/exhibit231-sx1december2025.htm)</u> |
| 23.2\* | <u>[Consent of Gallagher, Briody & Butler (included in Exhibit 5.1)](exhibit51-posam.htm)</u> |
| 24.1 | <u>[Power of Attorney](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/miax-20251209.htm#ibc908347a620461d9dea54d21c6d548c_334)[(contained on the signature page to the](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/miax-20251209.htm#ibc908347a620461d9dea54d21c6d548c_334)[original](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/miax-20251209.htm#ibc908347a620461d9dea54d21c6d548c_334)[Registration Statement on Form S-1 (333-292028) filed with the SEC on December 9, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/miax-20251209.htm#ibc908347a620461d9dea54d21c6d548c_334)</u> |
| 107 | <u>[Calculation of Filing Fees (Incorporated by reference to Exhibit 107 to the Company's Registration Statement on Form S-1 (333-292028) filed with the SEC on December 9, 2025)](https://www.sec.gov/Archives/edgar/data/1438472/000162828025056175/miaxexfilingfees12925.htm)</u> |

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__________________

\*Filed herewith.

+Indicates management contract or compensatory plan.

#Indicates portions of this exhibit have been omitted in accordance with Item 601(a)(5) of Regulation S-K. The Registrant undertakes to furnish a copy of all omitted schedules and exhibits to the SEC upon its request.

≠Indicates portions of this exhibit have been omitted in accordance with Item 601(a)(6) of Regulation S-K.

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**SIGNATURES**

Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant has duly caused this Post-Effective Amendment No. 1 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in Princeton, New Jersey, on this 12th day of December, 2025.

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| | |
|:---|:---|
| **MIAMI INTERNATIONAL HOLDINGS, INC.** | **MIAMI INTERNATIONAL HOLDINGS, INC.** |
| By: | /s/ Thomas P. Gallagher |
|  | Thomas P. Gallagher |
|  | Chairman and Chief Executive Officer |

---

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Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 1 to the Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

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| | | |
|:---|:---|:---|
| **Signature** | **Title** | **Date** |
| /s/ Thomas P. Gallagher | Chairman and Chief Executive Officer <br>(*Principal Executive Officer*) | December 12, 2025 |
| Thomas P. Gallagher | Chairman and Chief Executive Officer <br>(*Principal Executive Officer*) | December 12, 2025 |
| /s/ Lance Emmons | Executive Vice President and Chief Financial Officer <br>(*Principal Financial and Accounting Officer*) | December 12, 2025 |
| Lance Emmons | Executive Vice President and Chief Financial Officer <br>(*Principal Financial and Accounting Officer*) | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Talal Jassim Al-Bahar | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| John Beckelman | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Lee Becker | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| David Brown | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Kurt M. Eckert | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Kenneth W. Lozier  | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Mark I. Massad | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Lisa Moore | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Mark F. Raymond | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Cynthia Schwarzkopf | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Murray Stahl | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| Paul V. Stahlin | Director | December 12, 2025 |
| \* | Director | December 12, 2025 |
| J. Gray Teekell | Director | December 12, 2025 |

---

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| | |
|:---|:---|
| \* By: | /s/ Barbara J. Comly |
|  | Barbara J. Comly |
|  | as Attorney-in-fact |

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## Exhibit 5.1

**Exhibit 5.1**

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| | | |
|:---|:---|:---|
| | **GALLAGHER, BRIODY & BUTLER** | |
| **KEVIN M. BRIODY** | **COUNSELLORS AT LAW** |  |
| **JONATHAN M. GRISCHUK\*** |  | \* **ALSO ADMITTED IN NY** |
| **WILLIAM H. QUIRK, III\*** | **PRINCETON FORRESTAL VILLAGE** |  |
| **COURTENAY C. HANSEN\*** | **116 VILLAGE BOULEVARD** |  |
|  | **Suite 310** |  |
|  | **PRINCETON, NEW JERSEY 08540** |  |
|  | **(609) 452-6000** |  |
|  | **Fax: (609) 452-0090** |  |

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December 9, 2025

Miami International Holdings, Inc.

7 Roszel Road, Suite 1A

Princeton, New Jersey 08540

Ladies and Gentlemen:

We have acted as counsel to Miami International Holdings, Inc., a Delaware corporation (the "Company"), in connection with the Registration Statement on Form S-1 (File No. 333-292028) (such registration statement, as amended through the date hereof, the "Registration Statement") filed by the Company with the Securities and Exchange Commission (the "Commission") under the Securities Act of 1933, as amended (the "Securities Act"), relating to the offer and sale by the selling stockholders named in the prospectus (the "Prospectus") included in the Registration Statement (the "Selling Stockholders") of up to 7,762,500 shares of the Company's common stock, par value $0.001 per share of the Company (the "Common Stock"), including up to 1,012,500 shares of Common Stock subject to the underwriters' option to purchase additional shares) (such shares, the "Shares"), as set forth in the Prospectus.

This opinion letter is being furnished in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act.

We have reviewed originals or copies of the Registration Statement, the Prospectus, the amended and restated certificate of incorporation and amended and restated bylaws of the Company, each as amended through the date hereof, and such other corporate records, agreements and documents of the Company, certificates or comparable documents of public officials and officers of the Company and have made such other investigations as we have deemed necessary as a basis for the opinion set forth below.

In rendering the opinion set forth below, we have assumed:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a.the genuineness of all signatures;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b.the legal capacity of natural persons;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c.the authenticity of all documents submitted to us as originals;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;d.the conformity to original documents of all documents submitted to us as duplicates or conformed copies;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;e.as to matters of fact, the truthfulness of the representations made in certificates or comparable documents of public officials and officers of the Company and the Selling Stockholders; and

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December 9, 2025

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f.with respect to the issuance of the Shares, the amount of valid consideration paid in respect of such Shares equaled or exceeded the par value of such Shares.

We have not independently established the validity of the foregoing assumptions.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that, the Shares have been validly issued, fully paid and are nonassessable.

Our opinion is limited to the General Corporation Law of the State of Delaware, and we do not express any opinion herein concerning any other law. This opinion letter speaks only as of its date.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to the use of our name under the caption "Legal Matters" in the Prospectus. In giving such consent, we do not hereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act, and the rules and regulations of the Commission promulgated thereunder.

Very truly yours,

/s/ GALLAGHER, BRIODY & BUTLER

GALLAGHER, BRIODY & BUTLER

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