In 1941 he helped to form a left-wing political party, the Movimiento Nacionalista Revolucionario (MNR). In the same year he became Minister of Finance (1941–44), but then went into exile until 1951. In 1952, when the MNR came to power, he became President of Bolivia (1952–56). During this time the tin-mines were nationalized, adult suffrage introduced, and many large estates broken up and transferred to Indian peasants. He was re-elected President (1960–64), when he reached an understanding with international financiers for the re-organization of the tin industry. He was elected for a third time in 1964, but was overthrown by the army and went into exile until 1971. Military government ended in Bolivia in 1982 and in 1985 he was re-elected President in succession to Dr Herman Zuazo. In spite of a drop in world tin prices and consequential economic problems for Bolivia, his government survived until 1989, when he was succeeded by Jaime Paz Zamora.