He was an army officer when the Brazilian Armed Forces seized power in 1964 and established the Brazilian military government, a military dictatorship which ruled the country from 1964 to 1985. He began his political career in Pará in 1964, when President Humberto de Alencar Castelo Branco, the country's first leader following the 1964 Brazilian coup d'état, appointed Passarinho as the Governor of Pará. Passarinho served as governor from 1964 to 1966, when he left the governor's office to take a seat in the Federal Senate. He would be succeeded in 1966 by his protege, Major Alacid Nunes.