Can a prenup or marriage agreement be set aside in British Columbia?

This answer covers the law of British Columbia.

Yes, but only in limited situations. A written agreement between spouses can override the usual rules on dividing family property and debt, and a court will set it aside only if the Family Law Act allows it. The rules apply to spouses whether married or not, and unmarried partners become spouses for property purposes only after living together in a marriage-like relationship for at least two years.

The protected set-aside rules apply to a written agreement with each spouse's signature witnessed by at least one other person, and the same person can witness both signatures. An unwitnessed agreement is not automatically void, because the court may still apply the rules if appropriate in all the circumstances. The court may act only if a listed circumstance existed when the agreement was made: failure to disclose significant property, debts or other relevant information, improper advantage of vulnerability, not understanding the agreement, or common-law grounds making a contract voidable. Even then, the court can decline if it would not make a substantially different order.

Separately, the court may act if an agreement is significantly unfair, considering time passed, the intention to achieve certainty and reliance on its terms. Support and child-related terms are tested differently.