A prenup can be signed anywhere. But it will be evaluated for legal validity based upon the law of the place where it is signed, unless it says otherwise, and the place where the divorce takes place.
If the prenup is not enforceable, the reason will generally not be merely that it was signed in another jurisdiction. But it might be valid or enforceable because the formalities required in the jurisdiction of the divorce were not met at the time it was signed (e.g. if financial disclosures were not made, or one spouse didn't have access to legal counsel).
For example, Colorado is one of two states that has adopted the latest version of the Uniform Premarital and Marital Agreements Act, which has provisions related to "governing law", "formation" and to "enforceability."
The governing law provision, Colorado Revised Statutes § 14-2-304, which is usually applied at the time of a divorce, states:
(1) The validity, enforceability, interpretation, and construction of
a premarital agreement or marital agreement are determined:
(a) By the law of the jurisdiction designated in the agreement if the
jurisdiction has a significant relationship to the agreement or either
party at the time the agreement was signed and the designated law is
not contrary to section 14-2-309 or to a fundamental public policy of
this state; or
(b) Absent an effective designation described in paragraph (a) of this
subsection (1), by the law of this state, including the choice-of-law
rules of this state.
The formation requirements are set forth at Colorado Revised Statutes § 14-2-306 which state:
A premarital agreement or marital agreement must be in a record and
signed by both parties. The agreement is enforceable without
consideration.
The enforcement provisions at Colorado Revised Statutes § 14-2-309 states:
(1) A premarital agreement or marital agreement is unenforceable if a
party against whom enforcement is sought proves:
(a) The party's consent to the agreement was involuntary or the result
of duress;
(b) The party did not have access to independent legal representation
under subsection (2) of this section;
(c) Unless the party had independent legal representation at the time
the agreement was signed, the agreement did not include a notice of
waiver of rights under subsection (3) of this section or an
explanation in plain language of the marital rights or obligations
being modified or waived by the agreement; or
(d) Before signing the agreement, the party did not receive adequate
financial disclosure under subsection (4) of this section.
(2) A party has access to independent legal representation if:
(a) Before signing a premarital or marital agreement, the party has a
reasonable time to:
(I) Decide whether to retain a lawyer to provide independent legal
representation; and
(II) Locate a lawyer to provide independent legal representation,
obtain the lawyer's advice, and consider the advice provided; and
(b) The other party is represented by a lawyer and the party has the
financial ability to retain a lawyer or the other party agrees to pay
the reasonable fees and expenses of independent legal representation.
(3) A notice of waiver of rights under this section requires language,
conspicuously displayed, substantially similar to the following, as
applicable to the premarital agreement or marital agreement:
"If you sign this agreement, you may be: Giving up your right to be
supported by the person you are marrying or to whom you are married.
Giving up your right to ownership or control of money and property.
Agreeing to pay bills and debts of the person you are marrying or to
whom you are married. Giving up your right to money and property if
your marriage ends or the person to whom you are married dies. Giving
up your right to have your legal fees paid."
(4) A party has adequate financial disclosure under this section if
the party:
(a) Receives a reasonably accurate description and good-faith estimate
of value of the property, liabilities, and income of the other party;
or . . .
(c) Has adequate knowledge or a reasonable basis for having adequate
knowledge of the information described in paragraph (a) of this
subsection (4).
(5) A premarital agreement or marital agreement or amendment thereto
or revocation thereof that is otherwise enforceable after applying the
provisions of subsections (1) to (4) of this section is nevertheless
unenforceable insofar, but only insofar, as the provisions of such
agreement, amendment, or revocation relate to the determination,
modification, limitation, or elimination of spousal maintenance or the
waiver or allocation of attorney fees, and such provisions are
unconscionable at the time of enforcement of such provisions. The
issue of unconscionability shall be decided by the court as a matter
of law. . . .
(8) A premarital or marital agreement, or an amendment of either, that
is not in a record and signed by both parties is unenforceable.
The enforcement provisions contemplate situations where one spouse (often called the "poor spouse") can enforce the agreement if desired, but the other spouse (often called the "rich spouse") cannot enforce it.
Colorado Revised Statutes § 14-2-310 meanwhile, sets forth certain prenuptial agreement provisions that aren't enforceable even if the execution of the agreement meets all of the requirements:
(1) In this section, "custodial responsibility" means parental rights
and responsibilities, parenting time, access, visitation, or other
custodial right or duty with respect to a child.
(2) A term in a premarital agreement or marital agreement is not
enforceable to the extent that it:
(a) Adversely affects a child's right to support;
(b) Limits or restricts a remedy available to a victim of domestic
violence under law of this state other than this part 3;
(c) Purports to modify the grounds for a court-decreed legal
separation or marital dissolution available under law of this state
other than this part 3;
(d) Penalizes a party for initiating a legal proceeding leading to a
court-decreed legal separation or marital dissolution; or
(e) Violates public policy.
(3) A term in a premarital agreement or marital agreement which
defines the rights or duties of the parties regarding custodial
responsibility is not binding on the court.
Colorado is more stringent than most U.S. states in the requirements it imposes to enforce prenuptial agreements, so an agreement that met its standards would be valid in almost every U.S. state. Most, but not all, U.S. states, have enacted an earlier version of the uniform act with fewer formal requirements.
