The Liberals need to win the next election "for the sake of Canadians," Stéphane Dion told Liberal MPs Monday in his first caucus meeting since becoming party leader.

Liberal MPs clapped and shouted their approval as Dion and his wife Janine Krieber stood at the front of the room, flanked by the seven defeated leadership contenders.

Conservative and Bloc Québécois opponents say they won't underestimate Liberal Leader Stéphane Dion.
(CBC)

"The leadership race is over. The enthusiasm of the Montreal convention is forever," declared Dion, who came from fourth place to defeat rival Michael Ignatieff in a fourth ballot on Saturday.

Dion, who outlined his priorities as leader, says Canadians face a clear choice between two very different parties in the upcoming election, widely expected to take place next spring.

In contrast to the Tories, the Liberals are the party of social conscience and the environment, he said.

Dion, who joked about his grasp of English, also took a swipe at Prime Minister Stephen Harper.

"The final issue is the style of leadership that we want,” he said. “A leader that is so much a control freak that is muzzling his ministers — maybe for good reasons — and inviting the staff to spy on them, or do we want collegial leadership with the dream team?"

"I am telling you that we need to win the next election for the sake of Canadians," he said.

The party also welcomed new Liberal MP Glen Pearson, who won a Nov. 27 byelection, defeating Green party leader Elizabeth May in the London, Ont., riding.

Dion, who faces the task of rallying the Liberals to fight the next election, says he has some sense of what he's up against when it comes to his Conservative opponents.

"It's very likely the next election will be a choice between short-term gain with long pain," he said. "That means Mr. Harper coming with seemingly attractive tax cuts and a vote of responsibility."

Toe line on same-sex marriage

Dion is expected to press MPs to toe the party line when it comes to same-sex marriage.

Harper plans to ask parliamentarians this week whether they want to revisit the same-sex marriage issue and return to the traditional definition of marriage as the union of one man and one woman.

Dion believes it's a mistake to revive the debate.

New world, same backpack

Dion's staff say the new leader's world has changed completely since Saturday when he was named the new leader of the Liberal party.

Despite the changes, however, one thing remains constant — Dion's choice of a knapsack instead of a briefcase. But now as Liberal Leader, he has someone to carry it around for him.

People who know Dion say he's reserved and not inclined to show his emotions, but if there was any sense of shock it had worn off Sunday night after his first full day on the job.

"I realize I am the leader. What I don't know is what is the life of a leader," said Dion.

'I realize I am the leader. What I don't know is what is the life of a leader.'— Stéphane Dion

"During 10 years I was answering questions in the House because I was a minister. Now I will have to ask questions to the prime minister."

With files from the Canadian Press