MEXICO CITY—The Mexican government Monday said its navy captured the alleged leader of the country's most violent drug-trafficking organization, an important victory for the new administration of Mexican President Enrique Peña Nieto.

Miguel Angel Treviño, the head of the Zetas crime organization, was captured in northern Mexico, Deputy Interior Minister Eduardo Sanchez said in a televised news conference. Mr. Treviño had taken over control of the feared crime group after leader Heriberto Lazcano was killed in a shootout with...