From 23 June 1976 he became interim Prime Minister after Pinheiro de Azevedo suffered a heart attack during his presidential campaign.

He remained Prime Minister of Portugal as an interim official for the rest of Pinheiro de Azevedo's mandate, when he was substituted by the democratically elected Mário Soares.

[2] To balance the predominant Macanese legislature, he proposed electoral reform that empowered the Chinese business community and elites.

[3] During his tenure, Costa twice threatened to pull out of Macao unilaterally amid tense debate on the year of Handover.

[4] He was the son of Américo de Almeida e Costa and wife Julieta da Conceição Leote and married in Viana do Castelo, Meadela, at the Chapel of São Vicente, on 11 January 1959 to Maria Claudiana da Costa de Faria Araújo (b. Viana do Castelo, Meadela, House of o Ameal, 17 May 1934), one of the fourteen children of a couple of Northern Portuguese Nobility, and by whom he had issue.