Cauchon first ran for public office in the 1988 federal election when he challenged Prime Minister Brian Mulroney in the riding of Charlevoix, however he was unsuccessful in this bid.
In the 1993 federal election Cauchon once again sought a seat in the House of Commons of Canada.
In this election he was elected in the Montreal riding of Outremont, he was re-elected in the 1997 and 2000 elections.

Cauchon was appointed Secretary of State for the Federal Office of Regional Development - Quebec by Prime Minister Jean Chrétien in 1996.
He became a full cabinet minister in 1999 when he was given the position of Minister of National Revenue.
On January 15, 2002, he became Minister of Justice and Quebec lieutenant.
As justice minister, Cauchon argued in cabinet in favour of same-sex marriage and the decriminalization of marijuana (indeed, when asked whether he had used marijuana in the past, he responded "Yes, of course").

 In 2009, Cauchon indicated he was interested in re-entering politics and running in his former riding of Outremont, which was then held by New Democratic Party (NDP) Deputy Leader Thomas Mulcair.
The Liberal Party's Quebec Lieutenant Denis Coderre, who was tasked with finding Quebec candidates for the next election, announced that the riding was closed off to Cauchon and was being reserved for a female candidate.
Liberal leader Michael Ignatieff originally sided with Coderre in opposing Cauchon return, and instead planned to appoint prominent businesswoman Nathalie le Prohon as the candidate in the riding.
However, after facing pressure from within his caucus Ignatieff reversed his earlier decision and decide to allow Cauchon to seek the nomination, after Le Prohon indicated she would seek the Liberal nomination in Jeanne-Le Ber.
The controversy over the nomination led to Coderre's resignation as the Liberal's Quebec Lieutenant and Defence Critic, saying he no longer had the "moral authority" to continue.

In the federal election held on May 2, 2011,  Cauchon was unsuccessful in his bid to unseat Mulcair.
The NDP's support in Quebec, and throughout most of Canada, had surged in the final weeks of the campaign, at the expense of the Liberals and Bloc Québécois.
The NDP won 59 seats in Quebec and replaced the Liberals as the Official Opposition in the House of Commons.
Ignatieff had also failed in his bid to win re-election and resigned as party leader days later.
Cauchon first ran for public office in the 1988 federal election when he challenged Prime Minister Brian Mulroney in the riding of Charlevoix, however he was unsuccessful in this bid. In the 1993 federal election Cauchon once again sought a seat in the House of Commons of Canada. In this election he was elected in the Montreal riding of Outremont, he was re-elected in the 1997 and 2000 elections.
Cauchon was appointed Secretary of State for the Federal Office of Regional Development - Quebec by Prime Minister Jean Chrétien in 1996. He became a full cabinet minister in 1999 when he was given the position of Minister of National Revenue. On January 15, 2002, he became Minister of Justice and Quebec lieutenant. As justice minister, Cauchon argued in cabinet in favour of same-sex marriage and the decriminalization of marijuana (indeed, when asked whether he had used marijuana in the past, he responded "Yes, of course").
 In 2009, Cauchon indicated he was interested in re-entering politics and running in his former riding of Outremont, which was then held by New Democratic Party (NDP) Deputy Leader Thomas Mulcair. The Liberal Party's Quebec Lieutenant Denis Coderre, who was tasked with finding Quebec candidates for the next election, announced that the riding was closed off to Cauchon and was being reserved for a female candidate. Liberal leader Michael Ignatieff originally sided with Coderre in opposing Cauchon return, and instead planned to appoint prominent businesswoman Nathalie le Prohon as the candidate in the riding. However, after facing pressure from within his caucus Ignatieff reversed his earlier decision and decide to allow Cauchon to seek the nomination, after Le Prohon indicated she would seek the Liberal nomination in Jeanne-Le Ber. The controversy over the nomination led to Coderre's resignation as the Liberal's Quebec Lieutenant and Defence Critic, saying he no longer had the "moral authority" to continue.
In the federal election held on May 2, 2011,  Cauchon was unsuccessful in his bid to unseat Mulcair. The NDP's support in Quebec, and throughout most of Canada, had surged in the final weeks of the campaign, at the expense of the Liberals and Bloc Québécois. The NDP won 59 seats in Quebec and replaced the Liberals as the Official Opposition in the House of Commons. Ignatieff had also failed in his bid to win re-election and resigned as party leader days later.
Martin Cauchon