Upon his election, Singh became the first person of a visible minority group to lead a major Canadian federal political party on a permanent basis, and the second overall after the Bloc Québécois’s former interim leader Vivian Barbot.

[18] Singh was born on January 2, 1979[19][20] in the city of Scarborough, Ontario, now a district of Toronto, to Indian immigrants, Harmeet Kaur and Jagtaran Dhaliwal.

[25] After a year as a toddler living with his grandparents in India, Singh spent his early childhood in St. John's and Grand Falls-Windsor, both in Newfoundland and Labrador, before relocating with his family to Windsor, Ontario.

[26][27] Singh has publicly discussed suffering sexual abuse as a child from a martial arts coach, as well as having a father who struggled with alcoholism.

Singh called for greater police accountability and demanded the provincial government draft legislation to strengthen Ontario's Special Investigations Unit (SIU).

Singh said, "The comprehensive failure of the ministry to address concerns about the SIU and give it a proper mandate is simply unacceptable, and I expect immediate action from the new Attorney General.

[52] Singh's proposed legislation would give the Ontario Ombudsman the jurisdiction to investigate the practices of the corporation, as well as force Tarion to produce a detailed track record of their builds, and include all of their employees who make over $100,000 on the sunshine list.

[53] In October 2015, Singh introduced a motion calling on the government to instruct police services in Ontario to end arbitrary street checks, known as carding.

"[57] In June 2015, Singh was chastised by the integrity commissioner for the improper use of legislative resources meant for his constituency office for partisan purposes.

[58] In December 2016, Singh spoke out against the motion introduced by Progressive Conservative MPP Gila Martow, which called for the legislature to denounce the Boycott, Divestment and Sanctions campaign.

[62] Following the death of communist dictator Fidel Castro in October 2017, Singh tweeted "He saw a country wracked by poverty, illiteracy & disease.

[68] A poll by Mainstreet Research was released in September, showing Singh overtaking Charlie Angus to lead the race for the first time with 27.3 per cent of the vote.

[75] In a December 2017 interview with Bloomberg, Singh explained that he would not rule out working with the Conservatives to topple a federal government led by Trudeau if the NDP held the balance of power in a minority parliament.

Weir was formally expelled from caucus on May 3, 2018, based upon the outcome of the sexual harassment investigation which stated Weir's conduct was described by an investigator as “on the low-end of the scale,” and which would not normally be understood as “sexual harassment.” It was alleged he argued excessively over carbon levies with a staffer of then party leader Tom Mulcair's during a NDP convention and also he stood too close when speaking to people.

However, the incumbent Trudeau Liberal government failed to retain its majority, allowing the NDP to share the balance of power in Parliament.

[85] On June 17, 2020, Singh was removed from the House of Commons for the rest of the day after he called Bloc Québécois MP Alain Therrien a "racist" and refused to apologize when Therrien was the sole member to prevent unanimous consent on the second motion concluding systemic racism and discrimination in the Royal Canadian Mounted Police (RCMP) prior to the completion of the public inquiry from Singh's first motion.

[86] In the 2021 federal election campaign Singh was proud to announce that he was the only leader with a plan to enforce mandatory COVID-19 vaccination for employees that work under a collective bargaining contract.

The pact was influenced when the Freedom Convoy caused Trudeau to invoke and revoke the Emergencies Act over the vaccine mandate policy then in effect and also by the 2022 Russian invasion of Ukraine.

[94] On September 4, 2024, Singh announced that he was ending the 2022 confidence-and-supply agreement, citing discontent with the Liberals' performance on healthcare reforms and affordability measures.

[95][96] Later in the month the NDP faced two competitive federal by-elections in Elmwood—Transcona in Winnipeg and LaSalle—Émard—Verdun in Montreal,[97] winning the former and significantly improving their vote share in the latter.

This would be done by assisting provinces with the 2030 "coal phaseout", implementing a zero emissions vehicle agenda, "greening" the tax system by adding subsidies to companies supporting ecology and building a renewable energy super grid.

[107] Singh also supports creating more accountability in climate change policy by creating an independent officer of parliament mandated to report on interim progress on emission reductions (Climate Change Action Officer or CCAO), tasking the Commissioner of Environment and Sustainable Development (CESD) to the Auditor General with gathering data from each province and territory and appointing an advisory group composed of regional and topic-specific experts who will support the CCAO in interpreting data presented by the CESD and assessing implications for climate, energy, and economic policies and regulations.

"[111] In a 2011 interview with Jus Reign, then-federal candidate Singh gave as one of his reasons for entering politics as being to oppose recent comments made by the former premier of British Columbia and federal cabinet minister, Ujjal Dosanjh, himself a Sikh.

[112] Singh "spent much of his early political career as an MP in Ontario lobbying the province to recognize India's 1984 anti-Sikh riots as an act of genocide".

[121] Singh initially supported Kitimat's LNG Canada facility supplied by the Coastal GasLink Pipeline in British Columbia that would impact native burial grounds and override unceded lands such as the Wetʼsuwetʼen.

After the NDP lost Nanaimo in a May 2019 by-election to the Green Party, Singh quickly changed his position to oppose the LNG natural gas facility.

[127] Recounting a personal experience where he was the subject of racial profiling, Singh has strongly supported legislation for a federal ban on carding, calling the practice a form of systemic racism.

[128][129] When asked at NDP leadership debate in Saskatoon if he would bring back the long-gun registry Singh responded: "It's a difficult question, absolutely.

[136] In a November 2017 episode of the TVOntario series Political Blind Date, Singh was paired with former Toronto City Councillor and then-future Premier of Ontario Doug Ford.

[139] In January 2018, Singh became engaged to Gurkiran Kaur Sidhu, a fashion designer and co-founder of Jangiiro, a Punjabi clothing line.