The New Democratic Party was created in 1961 by Canadian labor unions.
The highest number of House of Commons seats that the party has won at any general election was 43, in 1988. They then sank to an all-time low of nine seats at the next general election, in 1993.
As a result they have, of course, not come near becoming the governing party. However, they have been a key faction during periods of Liberal minority government under Pierre Trudeau and Paul Martin.
The party has a left-wing populist platform, as described here.
Jack Layton has led the NDP since 2003.