Mr Dion was not his party's initial favourite for the post of leader
Stephane Dion's election as leader of the Liberal Party in 2006 was a surprise to many.
He was described as a man of principle and conviction "and therefore almost certain not to be elected leader of the Liberal party".
In the first round, he finished third with just under 18% of the vote.
As leader, he has maintained his reputation for integrity, but also raised concerns about his ability to lead the Liberals to victory.
Mr Dion's campaign in the 2008 general election has focused on green issues, pledging to act on Canada's Kyoto protocol commitments.
The party main proposal has been to create a carbon tax to cut greenhouse gas emissions, the cost of which would be offset by income tax cuts.
Known as the Green Shift, his political rivals have attacked it, saying it would trigger a recession.
Mr Dion was born in 1955 in Quebec City.
The former Quebec separatist, now a committed federalist, graduated received his doctorate in sociology in 1986 from the Institut d'Etudes Politiques in Paris.
He taught public administration and political science at the University of Montreal from 1984 to 1996, and was a visiting professor at the Brookings Institution in Washington, at the Laboratoire d'Economie Politique in Paris.
A star candidate in a by-election in 1996, he was appointed to the cabinet before being elected. He won re-election in 1997, and has been in parliament since then in a safe Liberal seat.
He served as a cabinet minister under former prime ministers Paul Martin and Jean Chretien, most notably as minister for the environment.
While the minority Conservative government needed opposition support to pass legislation in parliament, as leader of the Liberals, Mr Dion avoided confrontations in parliament that could have triggered an early election.
Finally, the decision was taken out of his hands when Prime Minister Stephen Harper called an early poll for 14 October.