Born in a village in the Jalandhar district of Punjab, India, Dosanjh emigrated to the United Kingdom at the age of 17 before moving to Canada almost four years later.

Dosanjh gained an early interest in politics from listening to debates between his father, a follower of Jawaharlal Nehru and Indian National Congress, and his grandfather, a former British Raj freedom fighter and socialist.

During this time he taught English as a second language courses at Vancouver Community College and worked as an assistant editor of a local Punjabi newspaper.

[7] His involvement with community organizations included founding the Farm Workers’ Legal Information Service (later Canadian Farm Workers' Union), serving on the board of directors for BC Civil Liberties Association and the Vancouver Multicultural Society, and the Labour Advocacy Research Association, as well as volunteer work with MOSAIC Immigrant Services Centre, and the South Vancouver Neighbourhood House.

[6][9] He was targeted again, on 26 December 1999, while he was a member of the Legislative Assembly of British Columbia, when his constituency office was broken into and a Molotov cocktail left burning on a table.

In April 2000, his middle son, Aseem, was charged with assaulting an Ontario police officer during a bar brawl, but was found not guilty.

[16] A month later, in a small cabinet shuffle upon the resignation of Moe Sihota, Harcourt added Minister Responsible for Multiculturalism and Human Rights to Dosanjh's portfolio.

On March 4, after the Royal Canadian Mounted Police (RCMP) raided the Premier's house, they briefed Attorney General Dosanjh, whose office had to assist, and placed him under a gag order.

Dosanjh's actions were variously criticized for not informing his party caucus and not going public sooner, and applauded for avoiding perceptions of conflict of interest despite his power to intervene.

Dosanjh was among the front runners, along with Corky Evans, Gordon Wilson, and Joy MacPhail who all had served at various cabinet posts.

[23] As Premier for two and a half sessions of the 36th Parliament, between February 24, 2000 and June 5, 2001, Dosanjh gave priority to issues of health care, education, and balanced budgets.

A boost in government revenue from rapidly expanding oil and gas development,[24] led Dosanjh to direct the Finance Minister to draft balanced budget legislation.

[25] However, the BC NDP were deeply unpopular within the province, reaching a low at 15% support in opinion polls at the time of Glen Clark's resignation as Premier in August 1999.

[24] Dosanjh was consistently ranked higher personal popularity over opposition leader Gordon Campbell until the run-up to the May 16, 2001 provincial election.

[clarification needed][29][30] Dosanjh and the BC NDP knew they would not be reelected, so they concentrated their campaign to a few ridings in the Lower Mainland which were still considered competitive.

[6][30] Dosanjh conceded defeat a week before the election, but requested voters consider making the NDP a strong opposition party.

[32] After the vote on May 16, Dosanjh lost his seat in Vancouver-Kensington along with all but two members of his Cabinet in the second-worst defeat of a sitting provincial government in Canada.

[33] In March 2004, with a federal election expected in the spring or summer, Prime Minister Paul Martin approached Dosanjh to be a candidate for the Liberal Party of Canada.

[37] Dosanjh introduced legislation to make cigarettes fire safe,[38] new regulations to further limit lead content in children's jewelry,[39] and supported an NDP motion to ban trans fats.

[42][43] Supported by a unanimous vote in the House of Commons, the government agreed to compensate the 6,000 Canadians infected with hepatitis C from tainted blood transfusion.

[50] The Law Society reviewed the affair and concluded that Grewal had attempted to elicit rewards for his compliance but cleared Dosanjh and Murphy of misconduct charges.

He was attended by fellow MP Carolyn Bennett, who is also a doctor, and he was rushed to hospital where a successful operation to remove a blood clot near his heart was performed.

[58] In the 40th Canadian Parliament, with his party once again forming the official opposition, Dosanjh was appointed the National Defence critic for the first parliamentary session which was short-lived.

[59] When Dion resigned as party leader, Dosanjh considered but did not run for leadership citing his inability to speak French and again supported Rae's bid.

Dosanjh introduced private member bill C-467 An Act to amend the Citizenship Act (children born abroad) in the 2nd session, and re-introduced it in the 3rd session where it received 2nd reading in September 2010, which would grant natural citizenship to children born to, or adopted by, Canadian citizens working for the federal government (including members of the Canadian Forces).