The son of a courier at the Banque de France, Delors himself joined the bank in 1945, later earning a degree in economics from the Sorbonne. He became active in the Christian Trade Union Confederation (renamed the Democratic Trade Union Confederation in 1964) and was named its economic adviser in 1950. In 1962 he left the Banque de France, where he had quickly risen to an executive position, to head the social affairs division of the state's General Planning Commission. From 1969 to 1972 he served as chief adviser on social affairs to the “new society” program of Prime Minister Jacques Chaban-Delmas.

Delors joined the Socialist Party in 1974 and in 1976 became the party's national delegate for international economic relations. In 1979 he was elected to the European Parliament, where he served as chairman of the economic and monetary committee. In 1981 President François Mitterrand (Mitterrand, François) appointed Delors minister of economics and finance. The French economy was then in recession, and Delors initially carried out the Socialist recovery plan of increasing government controls and spending. He eventually convinced Mitterrand to accept his program of austerity, however, which succeeded in restoring relative economic stability.

Delors left government to become the president of the European Commission in 1985. He revitalized the long-stalled EC, pushing through reforms and persuading the member states to agree to the creation of a single market, to take effect from January 1, 1993, the first step toward full economic and political integration. When his term expired in 1995, he was considered a leading contender for the French presidency that year, but he declined to run.