Can a same-sex couple both be listed as legal parents on a birth certificate without adoption?

Yes, in most cases. Ontario's parentage rules recognize a birth parent's spouse or partner as a legal parent where a child is conceived through assisted reproduction, without requiring that partner to adopt the child — this applies whether the couple is male-female or same-sex, provided the legal requirements for that route are met, such as the pregnancy resulting from assisted reproduction and the partner's intention to be a parent. Where both intended parents are recognized this way, both can be listed on the birth registration and the resulting birth certificate directly, without a step-parent adoption.

Adoption becomes relevant in situations that fall outside this framework — for example, where one partner is not recognized as a parent under the assisted reproduction rules and the couple instead wants that partner to acquire parental status through a step-parent adoption after the fact. Because the rules turn on specific facts, same-sex couples planning a pregnancy through a clinic or a known donor should confirm with a lawyer, before or shortly after conception, that their situation fits the automatic parentage route.