He was born one of the eleven children of António José Gomes (Chaves, Santo Estêvão - Lisbon, Socorro, 1 July 1922) and wife (m. Chaves, 17 January 1901) and wife Idalina Júlia Monteiro da Costa (Chaves, 27 May 1880 - Porto, 18 February 1967).

On 8 December 1952, Gomes married Maria Estela Veloso de Antas Varajão (born 23 March 1927 in Viana do Castelo), daughter of João de Campos Varajão and his wife Angélica Martins Veloso (b. Barcelos, Barcelos), at the See of Viana do Castelo. The couple had only one son, Francisco da Costa Gomes.

Costa Gomes was involved in a revolutionary attempt in 1961 led by the Minister of Defense, General Botelho Moniz. In 1970 he occupied the post of Commander of the Military Region of Angola where he overhauled the chief - command and was the first to try to establish a military agreement with UNITA against the MPLA and the FNLA.

On 12 September 1972 he was called back to Portugal to occupy the post of Chief of the Armed Forces, replacing General Venâncio Deslandes. However he was replaced in March 1974, a few days before the Carnation Revolution of April 25th 1974, because he had refused to swear his loyalty to the President of the Council of Ministers Marcello Caetano in a public ceremony.

After the Revolution, he was one of the seven military leaders who made up the National Salvation Junta. Between 25 April and 30 September he was the second in command of the Portuguese state behind António de Spínola.

He assumed the Presidency of the Republic when named by the Junta after the resignation of Spínola on September 30, 1974 and occupied the post until June 27, 1976 when in the first Presidential election the Portuguese chose General Ramalho Eanes to succeed him.