Is it too late to sign a marriage contract after we are already married in Ontario?

No, it is not too late. Ontario's Family Law Act permits spouses to enter into a domestic contract at any time — before marriage, on the day of marriage, or at any point during an existing marriage. Agreements signed during an existing marriage are sometimes called postnuptial agreements in everyday language, but they are legally the same type of domestic contract as a prenup.

That said, agreements signed during a marriage face a higher degree of scrutiny in some respects. Courts look carefully at whether one spouse was under pressure or whether there was a significant power imbalance at the time of signing. If the agreement was negotiated when the marriage was in serious difficulty, a court might view the circumstances as one in which meaningful consent was harder to establish.

The formal requirements are the same: the agreement must be in writing, signed by both spouses, and witnessed. Both parties should have independent legal advice and exchange full financial disclosure. A postnuptial agreement is often used when circumstances change significantly — for example, one spouse starts a business, receives a large inheritance, or the couple's financial situation shifts substantially enough that they want to re-set expectations going forward.