<Page>
                                                                    EXHIBIT 5.1



_______________, 2006

Tailwind Financial Inc.
BCE Place, 181 Bay Street
Suite 4400
Toronto, Ontario, Canada M5J 2T3

RE:  INITIAL PUBLIC OFFERING OF UNITS

Dear Sir or Madam:

We have acted as counsel to Tailwind Financial Inc., a Delaware corporation (the
"COMPANY"), in connection with the Company's Registration Statement on Form S-1,
as amended (the "REGISTRATION STATEMENT"), filed by the Company with the
Securities and Exchange Commission under the Securities Act of 1933, as amended.

The Registration Statement covers the registration of (i) 12,500,000 units (the
"UNITS") issuable to the public, each Unit consisting of (a) one share of the
Company's common stock, $.01 par value per share (the "COMMON STOCK"), and (b)
one warrant to purchase one share of Common Stock at an exercise price of $6.00
per share (the "PUBLIC WARRANTS"), (ii) an option (the "PURCHASE OPTION") to
purchase 625,000 units (the "PURCHASE OPTION UNITS") issued to Deutsche Bank
Securities Inc. (the "UNDERWRITER"), each Purchase Option Unit consisting of (a)
one share of Common Stock and (b) one warrant to purchase one share of Common
Stock at an exercise price of $7.20 per share (the "PURCHASE OPTION WARRANTS,"
and together with the Public Warrants, the "WARRANTS"), (iii) up to 1,875,000
Units (the "OVER-ALLOTMENT UNITS") that the Underwriters will have a right to
purchase from the Company to cover over-allotments, if any, (iv) the Purchase
Option Units issuable upon exercise of the Purchase Option, (v) all shares of
Common Stock and all Warrants issued as part of the Units, the Over-Allotment
Units and the Purchase Option Units and (vi) all shares of Common Stock issuable
upon exercise of the Warrants included in the Units, the Over-Allotment Units
and the Purchase Option Units.

In connection with this opinion, we have examined originals or copies of the
following documents (the "TRANSACTION DOCUMENTS"):

     (a)  the Registration Statement;

     (b)  the Purchase Option;

     (c)  the Warrant Agreement between the Company and American Stock Transfer
          & Trust Company as warrant agent (the "WARRANT AGENT");

     (d)  the Warrants; and

     (e)  such other documents as we have deemed necessary or appropriate to
          enable us to render the opinion expressed below.
<Page>

Tailwind Financial Inc.
_______________, 2006
Page 2


This opinion is based entirely on our review of the documents listed in the
preceding paragraph, and we have made no other documentary review or
investigation of any kind whatsoever for purposes of this opinion. In our
examination, we have assumed (i) the genuineness of all signatures, the
conformity to the originals of all documents reviewed by us as copies, the
authenticity and completeness of all original documents reviewed by us in
original or copy form, and the legal competence of each individual executing any
document; and (ii) that the Warrant Agreement is a legal and binding obligation
of the Warrant Agent. As to all matters of fact (including factual conclusions
and characterizations and descriptions of purpose, intention or other state of
mind) we have relied entirely upon the certificates of officers of the Company
and have assumed, without independent inquiry, the accuracy of those
certificates.

Subject to the limitations set forth below, we have made such examination of law
as we have deemed necessary for the purpose of this opinion. This opinion is
limited solely to the federal laws of the United States, the Delaware General
Corporation Law, including all applicable provisions of the Delaware
Constitution and reported judicial decisions interpreting these laws and, as to
the Warrants and the Purchase Option Units constituting valid and legally
binding obligations of the Company, solely to the laws of the State of New York.
Our opinion is based on these laws as in effect on the effective date of the
Registration Statement.

We note that certain of the Transaction Documents contain provisions stating
that they are to be governed by the laws of the State of New York (each
contractual choice of law clause being referred to as a "Chosen-Law Provision").
Except to the extent that such a Chosen Law provision is made enforceable by New
York General Obligations Law Section 5-1401, as applied by a New York state
court, or a federal court sitting in New York and applying New York choice of
law principles, no opinion is given herein as to any Chosen-Law Provision or
otherwise as to the choice of law or internal substantive rules of law that any
court or other tribunal may apply to the transactions contemplated by the
Transaction Documents.

Based upon and subject to the foregoing, we are of the opinion that

     1.   The Common Stock included in the Units, the Over-Allotment Units and
          the Purchase Option Units, when issued and sold in accordance with and
          in the manner described in the Registration Statement and related
          prospectus, will be duly authorized, validly issued, fully paid and
          non-assessable.

     2.   Each Warrant included in the Units, the Over-Allotment Units and the
          Purchase Option Units, when issued and sold in accordance with and in
          the manner described in the Registration Statement and related
          prospectus, will constitute a valid and binding agreement of the
          Company enforceable against the Company in accordance with its terms,
          except as enforcement may be limited by applicable bankruptcy,
          insolvency, reorganization, arrangement, moratorium, or other similar
<Page>

Tailwind Financial Inc.
_______________, 2006
Page 3


          laws affecting creditors' rights, and subject to general equity
          principles and to limitations on availability of equitable relief,
          including specific performance.

     3.   The Units, the Over-Allotment Units and the Purchase Option Units have
          been duly authorized.

     4.   The Purchase Option, when issued and sold in accordance with and in
          the manner described in the Registration Statement and related
          prospectus, will constitute a valid and binding agreement of the
          Company enforceable against the Company in accordance with its terms,
          except as rights to indemnity under the Purchase Option may be limited
          by applicable laws and except as enforcement may be limited by
          applicable bankruptcy, insolvency, reorganization, arrangement,
          moratorium, or other similar laws affecting creditors' rights, and
          subject to general equity principles and to limitations on
          availability of equitable relief, including specific performance.

     5.   The Common Stock, when issued and paid for upon exercise of the
          Warrants as contemplated by the Warrant Agreement, the Registration
          Statement and related prospectus, will be duly authorized, validly
          issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion with the Securities and Exchange
Commission as an exhibit to the Registration Statement and the reference to us
under the heading "Legal Matters" in the related prospectus.

Sincerely yours,





BINGHAM McCUTCHEN LLP