If I owned my home before marriage, does it become a protected matrimonial home once I marry?

Yes, generally. Once you marry and the couple ordinarily occupies the property as their family residence, it becomes a matrimonial home under Ontario's Family Law Act, regardless of the fact that you owned it before the marriage and regardless of whether your new spouse's name is ever added to title. Matrimonial home status is about how the property is actually used by the married couple, not about who bought it or when.

This has two significant consequences worth understanding upfront. First, your spouse gains the usual matrimonial home protections, including an equal right of possession and the requirement that they consent before the home is sold or encumbered, even though they have no ownership interest in it. Second, and often more surprising, the home doesn't get the usual credit for its pre-marriage value in the equalization calculation on separation, since the matrimonial home is treated as a specific exception to that general rule. Because bringing a pre-owned home into a marriage carries these consequences automatically, without any extra step required, anyone in this situation should get legal advice, ideally before marrying, if they want to understand or plan around how these rules will apply.