Arias Navarro was a hardline politician and was involved in the White Terror, having signed thousands of death warrants during the dismantling of the Spanish Republic.

After the assassination of Prime Minister (Presidente del Gobierno) Luis Carrero Blanco he was appointed his successor on 31 December 1973, a position he continued to hold after the death of Franco.

Franco's successor as head of state, King Juan Carlos I, continued his appointment, so that it was his government (which included Manuel Fraga Iribarne and José María de Areilza) that instituted the first reforms, however unwillingly.

In June 1977, during the first free general elections held since 1936, Arias joined the Alianza Popular, a right-wing party created by Manuel Fraga.

According to the Spanish daily El País,[11] files released by the US National Archives and Records Administration show that, following the left-wing Carnation Revolution in Portugal on 25 April 1974, Arias met with the United States Deputy Secretary of State Robert S. Ingersoll in March 1975 and offered to invade Portugal in order to stop the spread of communism.