Elected a city councilman in Santiago de Cuba, he quickly became a leader of the Liberal Party, and was befriended by Fulgencio Batista.

During General Batista's exile in the United States from 1944–1952, Rivero practised law in Cuba and wrote political commentary for several periodicals.

Elected a Senator from Pinar del Río Province in 1954, Rivero became Cuba's prime minister (1957–1958), and participated in several reconciliation conferences as Batista's representative.

Ambassador Earl E. T. Smith, and with leading Cuban politicians, to resolve the crisis caused by the ongoing rebellion led by Fidel Castro.

He apparently wished to convene a Constituent Assembly shortly after taking office, to bring about a restoration of constitutional rule.