Fabius announced Mauroy's death during a visit to Tokyo, Radio France International reported.
Mauroy was "a pillar of democratic socialism," said Fabius, who succeeded Mauroy as prime minister in 1984.
Family members said Mauroy was hospitalized June 1 in a state of extreme tiredness. He had undergone surgery for lung cancer in April 2012.
A former teacher, Mauroy was elected mayor of Lille in 1973, a post he held until 2001. He served as a member of the European Parliament between 1979-1980 and was named prime minister of France in 1981.