New York's highest court expanded the definition of parenthood Tuesday by ruling that former same-sex couples may seek visitation and custody of children even when they aren't the biological or adoptive parent.

The Court of Appeals decision resolves two cases of former unmarried same-sex couples in which the biological mothers kept the children and their ex-partners sought legal standing to see them. In one case, lower courts ruled the ex-partner had no standing. In the other, the ex-partner pays child support and was later granted visitation.

A 25-year-old definition of parenthood required a person seeking custody or visitation to have a biological or adoptive connection to the child. In its decision, the court said the standard had become "unworkable" in light of society's "increasingly varied familial relationships."

"Where a partner shows by clear and convincing evidence that the parties agreed to conceive a child and to raise the child together, the non-biological, non-adoptive partner has standing to seek visitation and custody under Domestic Relations Law," reads the opinion written by Judge Sheila Abdus-Salaam.

New York began recognizing same-sex marriages in 2011, and children born into a marriage are considered the children of both parents. But the law was far murkier when it came to same-sex couples who had a child before the law was enacted or who have foregone marriage. Same-sex partners often found it impossible to seek visitation or custody of a non-biological child they had not adopted if the relationship ended.