We separated but never signed anything — can we still make an agreement now in Ontario?

Yes. Separated common-law or married partners in Ontario can enter into a domestic contract — specifically a separation agreement — at any time after separation. There is no requirement to reach a formal agreement on a specific timeline, though limitation periods on certain legal claims mean delay can cost you remedies.

A separation agreement signed after the fact is subject to the same requirements as any domestic contract: it must be in writing, signed by both parties, and witnessed. The same grounds for setting aside an agreement apply — non-disclosure, duress, undue influence, or unconscionability — so even a post-separation agreement benefits from full financial disclosure and independent legal advice for each party.

If you have been living separately and managing informally without an agreement, a formal separation agreement still serves a valuable purpose: it creates certainty, is enforceable, and documents the arrangements you may already be following informally (such as a parenting schedule). Courts also generally prefer to see a comprehensive agreement rather than bits of informal arrangement. If there are disputes you cannot resolve, a mediator can help, and if mediation fails, either party can apply to the court.