Born in La Bouillie, Côtes-d'Armor, the son of tenant farmers, Hervé graduated in public law at the university of Rennes and also has a graduate degree in political science. He became a teacher in administrative law and in constitutional law in 1969. Hervé has a daughter and twin sons.
Hervé made his way in politics through activism and became the mayor of Rennes in 1977. He abandoned his job as a teacher to dedicate himself to his mandate. He started an innovative urban policy which he carried on fervently: social mix, support for cultural activities, ecology, development of public transportation (see Rennes Metro). On 20 January 2007, he announced that he would not apply for a 6th mandate as mayor of the city.
Hervé was elected for the first time as deputy during the legislative election in 1981. He became French Minister of Health (1981 / 1983–1986) and Minister of Energy (1981–1983). As Secretary of Health in the Fabius government, he was found guilty on 3 March 1999 by the court of justice of the Republic in the case of contaminated blood but has been dispensed from any punishment.