A $9 million nationwide class settlement resolving allegations that Post Holdings Inc. unit Premier Nutrition Corp. deceptively marketed protein shakes got the final nod.

Joseph Gregorio alleged “Premier Protein” ready-to-drink shakes contained less than the 30 grams of protein stated on the label. He and other consumers overpaid for the shakes because they were shortchanged by the ingredients, he said.

The U.S. District Court for the Southern District of New York tentatively approved the deal in in September and gave...