In 1935 he became mayor of Louviers in 1938 undersecretary of state at the treasury in the government of Leon Blum.
In World War II, he served in the air force, but after the German occupation of France in June 1940, fled to North Africa, where he was arrested for treason and sent back to France. He was imprisoned by the Vichy government at Clermont-Ferrand, but succeeded in escaping in June 1941 with the help of his wife and friends.
He reached England in 1942, and joined the Free French Air Force. From 1943 to 1945 he participated in Charles de Gaulle’s provisional government in Algeria as commissioner for finance.
In 1945 he was appointed minister of the economy, but his stringent anti-inflationary measures were opposed by other members of the government and he had to resign. The following year he was made governor of the Bank of Reconstruction and Development. In the same year he was reelected to parliament, where he made his mark with his criticisms of government policies on Indochina, Algeria, and the economy.
In 1954, following the fall of Dicn Bien Phu, he was elected prime minister by a huge majority on the strength of his undertaking to end the war in Indochina in a month and to introduce economic reforms. The former promise was fulfilled at the Geneva conference which agreed on an armistice line on the seventeenth parallel. He then formulated a plan for a European Defense Community with British participation. However his proposal to accord independence to Morocco and Tunisia was thought to have inspired the Algerian rebellion of October 1954 and early in 1955 his North African policies were rejected by parliament and he resigned the premiership.
For a few months in 1956 he was deputy premier without portfolio in Guy Mollet's government, but left over disagreements concerning North African policies. He tried to make his Radical party the key factor in the noncommunist left, but after his failure to be reelected to parliament in 1958, he resigned his leadership of the party. He returned to parliament in 1967 and the following year founded a new party, the Parti Socialiste Unifié. Thereafter he did not reattain a prominent political position, but remained a respected figure in French politics, greatly admired for his intellectual grasp. His books included The Pursuit of Freedom (1956) and Modern French Republic (1963).
He had ascetic tendencies and made a brave but unsuccessful attempt, while premier, to get his countryment to drink milk instead of wine.
He joined the Radical Socialist party when he was sixteen, and in 1932 became the youngest deputy ever elected to the National Assembly.
He left behind a letter addressed to Marshal Petain in which he wrote: “My escape is not the act of a condemned man who is running away from a punishment he deserves. It is, after using up all the legal means available to me, my last resort to proclaim once again, my refusal to submit to the lie of the judgment that has stricken me.
This judgment was not a decision of justice, it is not even a judiciary error, it is a political violation.... It is not the army officer that was condemned, it was the deputy, the man of the Left, the Jew, the patriot who refuses to accept the defeat of his country. Neither the law nor my conscience compel me to obey.”