John Gilbert "Jack" Layton, PC (Queens Privy Council for Canada), MP (List of House members of the 40th Parliament of Canada) (born July 18, 1950) is a Canadian (Canada) social democratic (Social democracy) politician, that has been the leader of the New Democratic Party since 2003. He is a former member of the Toronto City Council and acting deputy mayor of Toronto, Ontario. On June 28, 2004, he was elected Member of Parliament for the constituency of Toronto?Danforth. He is married to fellow MP Olivia Chow.

The son of a Progressive Conservative (Progressive Conservative Party of Canada) cabinet minister, Layton was raised in Hudson (Hudson, Quebec), Quebec. He rose to prominence in Toronto municipal politics where he was one of the most prominent left-wing voices on city and metro council, and was also a Board member for the Toronto Port Authority. In 1991 he ran for mayor, but lost to June Rowlands. Remaining on council he rose to become head of the Federation of Canadian Municipalities. In 2003 he was elected head of the NDP on the first ballot of the convention.

Under his leadership, the NDP considerably increased their support, almost doubling the partys popular vote in the 2004 election (Canadian federal election, 2004), though vote splitting with the Liberals limited their gain in seats. Laytons NDP held balance of power in Paul Martins minority government, where in May 2005 the NDP supported the Liberal budget in exchange for major amendments, in what was promoted as Canadas "First NDP budget". In November of that year, Layton worked with other opposition parties in bringing down the Liberal government over the findings of the Gomery Commission. The NDP saw further gains in the 2006 (Canadian federal election, 2006) and 2008 elections (Canadian federal election, 2008), in which the party won more seats than it had since its 1980s peak. The NDPs current tally of 37 MPs under Layton is just 6 seats short of the partys all-time high (Canadian federal election, 1988) under Ed Broadbent. According to a poll by Angus Reid Global Monitor, Layton is the best-ranked federal party leader in Canada.