SAN DIEGO—Mayor Jerry Sanders reversed his opposition to marriage for same-sex partners Sept. 19 and revealed that his adult daughter is a lesbian.

Sanders signed a San Diego City Council resolution supporting a challenge to California’s gay marriage ban. The Republican mayor said he could no longer back the position he took two years ago, when he said he favored civil unions but not full marriage rights for gay couples.

He fought back tears as he said he wanted his daughter and other gay people he knows to have their relationships protected equally under state laws.

“In the end, I could not look any of them in the face and tell them that their relationships—their very lives—were any less meaningful than the marriage that I share with my wife Rana,” Sanders said.