His administration, following the enactment of Institutional Act 5 (AI-5), marked the beginning of the harshest and most brutal phase of the military dictatorship, which was continued by General Emílio Garrastazu Médici, his successor.

Made an aspirant on January 18, 1921, he was commissioned 2nd Lieutenant in 1922 and was stationed with the 1st Infantry Regiment in Vila Militar until 5 July 1922, when he was involved in Tenentist rebellion and imprisoned for six months.

As part of a joint program, he was trained in the United States of America from January to June 1944, after having been an assistant instructor of general tactics at the School for Command and the Army General-Staff.

During the presidency of João Goulart, Costa e Silva put down left-wing student demonstrations that broke out in the Northeast and subsequently was removed from command of the 4th Army.

After the 1964 Brazilian coup d'état Costa e Silva was appointed the Minister of War on 1 April 1964, and remained in that post during the presidency of Castelo Branco.

While Costa e Silva was campaigning for the presidency of the republic, he barely escaped death during a left-wing guerrilla attack at Guararapes International Airport in Recife on 25 July 1966.

Since the airplane that was supposed to take him had broken down earlier that day in João Pessoa, Costa e Silva decided to leave Recife by automobile, thereby avoiding the assault which left several men dead or injured in what became known as the Attack of the Guararapes.

It also instituted heavy-handed censorship, abolished habeas corpus for political crimes, and gave the federal government nearly unlimited authority to intervene in state and local affairs.

Almost as soon as Costa e Silva signed this decree, he used its provisions to close Congress, as well as the legislatures of all states except São Paulo, and assumed full legislative powers.

Mário Kozel Filho, a soldier who was completing his compulsory military service and serving as a sentry on that day, left his post and ran towards the vehicle, trying to see if anyone was trapped inside.

Although civilian Vice President Pedro Aleixo should have succeeded him, the three armed forces ministers instead took power as a military junta under the 12th Institutional Act.

Due to the heavy press censorship of the time, many people did not accept the official version of events about Costa e Silva's illness, instead believing that he had been removed by the more conservative elements of the military regime.