What formalities are required for a cohabitation agreement to be legally valid in Ontario?

Under Ontario's Family Law Act, a domestic contract — including a cohabitation agreement — must meet three formal requirements to be valid: it must be in writing, signed by both parties, and witnessed. These requirements are straightforward but sometimes overlooked.

"In writing" means the entire agreement must be documented and readable. Verbal agreements about property or support are not enforceable as domestic contracts. "Signed by both parties" means both partners must physically or electronically sign the document — electronic signatures are generally acceptable for domestic contracts in Ontario following recent updates to electronic document law, though some lawyers prefer wet (paper) signatures for greater certainty. "Witnessed" means that at least one witness observes each signature — the witness should not be one of the parties themselves and ideally should not be a close family member who might later be challenged.

Beyond these statutory minimums, best practice adds: full financial disclosure exchanged before signing; each party having independent legal advice from their own lawyer; and enough time between the draft being provided and the signing date for each party to read and understand it. None of these additional steps are required by statute, but they dramatically reduce the risk that the agreement will be set aside.