Gilles Duceppe (French pronunciation: [ʒil dzysɛp]; born July 22, 1947) is a Canadian retired politician, proponent of the Quebec sovereignty movement and former leader of the federal political party, Bloc Québécois. He was a Member of Parliament in the House of Commons of Canada for over 20 years and was the leader of the sovereigntist Bloc Québécois for 15 years in three stints: 1996, 1997–2011 and in 2015. He was Leader of the Official Opposition in the Parliament of Canada from March 17, 1997, to June 1, 1997. He resigned as party leader after the 2011 election, in which he lost his own seat to New Democratic Party (NDP) candidate Hélène Laverdière and his party suffered a heavy defeat; however, he returned four years later to lead the party into the 2015 election. After being defeated in his own riding by Laverdière again, he resigned once more.

Duceppe was born in Montreal, Quebec, the son of Hélène (née Rowley) and actor Jean Duceppe. His maternal grandfather was John James Rowley, British by birth, Irish by descent, and a home child. Duceppe once joked about his British roots, saying, "I'm a bloke who turned Bloc."

Duceppe has told the story of an anglophone Grade 6 teacher slapping him after he complained about preferential treatment being given to anglophone students. Duceppe claimed he slapped the teacher back. He became a sovereigntist by the age of 20, inspired by René Lévesque and the founding of the Mouvement Souveraineté-Association.

Duceppe completed his high school studies at the Collège Mont-Saint-Louis. He then studied political science at the Université de Montréal but did not complete his program of study. While attending the Université de Montréal, he became general manager of the school's newspaper, Quartier Latin. In his youth, he advocated communism, and held membership in the Workers' Communist Party of Canada (WCP), a Maoist group. Duceppe later claimed that his three-year membership in the WCP was a mistake brought on by a search for absolute answers.

However, during this period (which lasted well into his thirties) he subscribed to militant Maoist ideology and was fired from his job as a hospital orderly for belligerent activities. Duceppe even went so far as to intentionally spoil his 1980 sovereignty-association referendum ballot arguing that Québécois should instead focus their efforts on staying united to fight capitalism.

Before becoming a member of Parliament, Duceppe worked as a hospital orderly and later became a trade union negotiator. In 1968 he became vice-president of the Union générale des étudiants du Québec (General Union of Quebec Students) and in 1970 manager of the Université de Montréal student paper, Quartier latin. In 1972 he launched his career in community and union settings, as moderator for the citizen's committee of Hochelaga-Maisonneuve, then in 1977 as a representative for the Royal Victoria Hospital employees. In 1981 he became a union organizer for the Confédération des syndicats nationaux (Confederation of National Trade Unions), where he became a negotiator in 1986.

In 1990, Duceppe was elected to the House of Commons of Canada in a by-election for the eastern Montreal riding of Laurier—Sainte-Marie. He defeated Liberal Denis Coderre, who would later serve alongside Duceppe in Parliament before becoming Mayor of Montreal. Duceppe would be handily re-elected at each election from 1993 to 2008.

Duceppe originally sat as an independent because the Bloc had not been registered by Elections Canada as a political party. All of the Bloc's other Members of Parliament had crossed the floor from either the Progressive Conservative Party or the Liberal Party earlier that year. Duceppe's victory demonstrated — for the first time — that the party had electoral support in Quebec and could win elections. Previously, many pundits (and members of other parties) predicted that the Bloc would not gain traction with ordinary voters in Quebec.