Médici was born in Bagé, Rio Grande do Sul state, he was the son of a family of Basque and Italian descent, who were originally from Paysandú, Uruguay. In the 1920s he entered in the Army where he was steadily promoted, becoming general in 1961.
Médici was a close ally of Marshal Artur da Costa e Silva, who became president of Brazil in 1967. Also in this year Médici was appointed chief of the National Information Service (SNI).
Two years later he become commandant of the Third Army when he was elected president of Brazil by the Congress, to succeed Costa e Silva, who was ill. Médici took oath on October 30, 1969 and served until the end of his term, March 15, 1974.
During his tenure, Médici established a strong military government, the more repressive of Brazil's military regimes, accompanied by tortures and strict censorship of the press. During his rule an existing guerilla activity was defeated , led by Carlos Marighela and Carlos Lamarca. The movement was destroyed and Marighela and Lamarca killed.