Trudeau said Saturday the Liberals were more concerned during that time with their own fate rather than that of Canadians.
He said that attitude illustrates why the party went from 172 seats in 2000 to its current 35-member caucus.
''The biggest problem was that we...started thinking more about ourselves than we did about Canadians,'' Trudeau said at a meeting of the party's Quebec wing in Victoriaville, Que.
He told reporters he believes he has changed that culture since becoming leader in April 2013.
''Despite all the media, the social media, the advertising, it's the work on the ground and the human contact that count,'' he said.
Trudeau refused to criticize his predecessors' policies over the last decade.
The Liberals have only eight of the 75 seats in Quebec and Trudeau acknowledged they have bridges to rebuild in the province.
''Not only will Quebecers be present in my government, they will be listened to.
''It won't just be a prime minister from Quebec but there will be ministers from Quebec in strong positions.''