Mauroy was born in Cartignies. A teacher, he led the Socialist Young Movement and the Technique Teaching Union in the 1950s. He became a leading figure in the Socialist federation of Norddépartement, which was among the third biggest of the SFIO party and climbed quickly in the party. In 1966, he became number 2 of the party behind the secretary general, Guy Mollet. Nevertheless, when Mollet resigned as leader in 1969, Alain Savary was chosen to succeed him.
After the electoral disasters of 1968 and 1969, he was persuaded of the necessity to renew the party. In 1971, during the Epinay Congress, he supported François Mitterrand's advent and became the number 2 in the Socialist Party (PS). Two years later, he was elected as a deputy and Mayor of Lille.
Progressively, he criticized the ejection of former SFIO members from the important functions in aid of Mitterrand's friends. In this, he formed an alliance with Michel Rocard, the main opponent of Mitterrand, during the 1979 Metz Congress. However, Mitterrand chose him as spokesperson during the 1981 presidential campaign; after Mitterand's election, he appointed Mauroy as Prime Minister.
His cabinet did important social reforms including reduction of the working time to 39 hours, retirement at 60 years and a rise in allowances. However, he advocated the abandonment of the socialist economic policy, which was ratified by President Mitterrand in March 1983. Failing to restrict the financing of private schools, he resigned in 1984.
In 1988, he became First Secretary of the PS against the will of Mitterrand, who supported Laurent Fabius. Until the end of his term, in 1992, he tried to appease the relations between the clans which composed the PS, notably during the very strained 1990 Rennes Congress. He allied with the rocardien group and Lionel Jospin's supporters, who came from the mitterrandist group.
President of the Socialist International from 1992 to 1999, Senator since 1992, he left the Lille belfry in 2001. Considered a moral authority of the French Left, he supported the candidacy of Ségolène Royal during the 2007 primary election.
29 June 1982 - Jean-Pierre Chevènement succeeds Dreyfus as Minister of Industry. Pierre Bérégovoy succeeds Questiaux as Minister of National Solidarity, becoming also Minister of Social Affairs.
Mauroy's Third Government, 22 March 1983 - 17 July 1984
