The ordinance requires McDonald's and other fast-food servings with toys to meet new nutritional standards.
Newsom had indicated he would veto the law. That veto would be meaningless because the board approved the ordinance 8-3, a veto-proof margin. With eight votes, the board could override the veto.
The new law, which San Francisco officials hope other cities will adopt in battling a child obesity epidemic, was a defeat for McDonald's, which led the fight against the measure.