 Following the passage of the Sáenz Peña Law to that effect, he was elected to Congress in 1912 on the UCR ticket, and to the Senate (1919-1923), always representing the city of Buenos Aires.In 1920, Gallo was one of the founding members of the Argentine Patriotic League, a far-right paramilitary organization.President Marcelo Torcuato de Alvear named Gallo Minister of Internal Affairs in 1923, and in 1924, he was part of a group of UCR members who broke with their longtime leader, the populist Yrigoyen, and formed the splinter Antipersonalist UCR.