Martin graduated from Argyle High School in 1974. He worked as a journeyman carpenter for several years, and was employed in forest service, mines and construction. Martin also served as business manager of the Manitoba Carpenters Union from 1989 to 1997, and was vice-president of the Manitoba Federation of Labour for a time. He has been an executive member of the Manitoba Building Trades Council, and was part of the Winnipeg 2000 Economic Development Committee.[citation needed]

Martin was first elected to the Canadian House of Commons in the 1997 federal election, defeating Liberal incumbent David Walker by a margin of 10,979 votes to 9,895. His riding of Winnipeg Centre, formerly known as Winnipeg North Centre, was successively represented from 1921 to 1984 by J.S. Woodsworth and Stanley Knowles, two of the most prominent social democratic politicians in Canadian history. Martin's victory over Walker returned the riding to the NDP for the first time since 1988.[citation needed] Martin was re-elected in the 2000 federal election, defeating Liberal Kevin Lamoureux by 11,263 votes to 9,310. He increased his margin of victory in the 2004 election, defeating Liberal candidate David Northcott by about 3,000 votes.

Martin has championed the rights of labour and aboriginal Canadians, and has spoken out against tax loopholes for private corporations.[citation needed] He supported Bill Blaikie for the NDP leadership in 2002-03.

He called for Svend Robinson to be removed from the NDP's foreign affairs portfolio in 2002, after Robinson's controversial visit to the Palestinian Authority.

Martin is an outspoken critic of the monarchy of Canada and has commented in favour of republicanism, both in parliament and in the media, citing the marriage of the Prince of Wales to the Duchess of Cornwall as a reason for the change.

When Liberal leadership candidate Joe Volpe received donations totalling $108,000 from Apotex executives and their wives and children, Martin suggested that these donations had the appearance of fraud. He filed an official complaint on May 29, asking elections commissioner Raymond Landry to investigate whether an attempt had been made to circumvent the Elections Act which banned corporate donations. Volpe responded by promising to return any donations that contravened the letter or spirit of the law.

In June 2008 MP Pat Martin introduced a motion into the House of Commons calling on the government to amend the coat of arms to incorporate symbols representing Canada's First Nations, Inuit and Métis peoples.

CBC chief correspodant Peter Mansbridge has referred to Martin as a "showboat"

In 2010, Martin stated that the social-service organization Youth For Christ were "evangelical fundamentalists" who were "preying on vulnerable kids". This statement was made when he was stating his opposition to funding an $11 million youth center being built on Winnipeg's Main Street by the organization. The Winnipeg Free Press called Martin's outburst irrational. Spokespeople from Aborginal organizations that work in inner-city areas have, however, noted that Youth for Christ is more evangelical than most faith-based charities and hostilely refers to non-Christians as "deniers".

On May 7th, 2010, Pat Martin was accused of tea-snatching from a parliamentary committee room by Conservative Party of Canada MP Dick Harris, who asked on a point of order: "Could I ask the clerk, with the agreement of the committee, to send him a letter, tell him to buy his own bloody tea?". Martin openly admitted as much. "I will confess to a proclivity towards green tea, and even to grazing the committee rooms in search of complimentary beverages." He went on to add that there was parliamentary precedent, citing former Member of Parliament Stanley Knowles' affection for Arrowroot biscuits and complementary tea bags.