He was a deputy in the National Assembly of France for the first district of Yonne for several terms between 1968 and 2012; mayor of Auxerre from 1971 to 1998; President of the Regional Council of Burgundy (1992–1993 and 1998–2004); and national minister of youth, labour, public administration and agriculture.

He first entered the government under the Presidency of his fellow party member Valéry Giscard d'Estaing when he became Secretary of State for Universities on 27 May 1974, serving that position until 12 January 1976.

He was Secretary of State near the Prime Minister, in charge of Vocational Training, from the latter date until 25 August 1976 and then Secretary of State near the Minister for Quality of Life, in charge of Youth and Sports, until 29 March 1977.

[1] After Socialist François Mitterrand's re-election as president seven years later, Soisson returned to the government, taking part in Mitterrand's so-called ouverture, i.e. inclusion of centre-right politicians in predominantly left-wing governments.

Later in that year he became Minister of Agriculture and Rural Development on 2 October, serving until 29 March 1993.

[1] However, his alliance with the National Front between 1998 and 2004 in order to keep his seat in the Regional Council of Bourgogne tarred his career, and owed him to be excluded from the Union for French Democracy (UDF), along with Charles Baur, Jacques Blanc, Charles Millon and Bernard Harang.

Soisson was appointed a Knight of the Legion of Honour in November 2016, for service during the Algerian War.