Rona Ambrose has been chosen as the Conservative Party's interim leader and says her team is prepared to work hard to return to power.

"I'm extremely proud to be leader of the Opposition," said the Alberta MP and former health minister.

Ambrose, 46, said the Conservative caucus has deep experience and diverse talent and will hold the new Liberal government to account while being "extremely constructive." She congratulated the Liberals on their successful campaign.

Ambrose has held eight different cabinet posts since 2006, including environment and public works.

Asked about the sharply partisan tone that characterized the Conservative Party in the past, Ambrose said, "Well, I'm here. I'm not sure if that's a reflection of a new tone, but my colleagues chose me, and they put their trust in me."

Harper speech 'well received'

Earlier in the day, outgoing leader Stephen Harper addressed the caucus in a speech that was "well received," according to sources. He took responsibility for the election defeat, and listened to others voice their thoughts on the campaign — both good and bad.

Ambrose described Harper's address as "incredibly passionate, emotional and touching" as he said his goodbyes.

 "We had a wonderful meeting where we were able to hear from our colleagues that aren't with us any longer, incredibly gracious comments, and the biggest message of all was that we have an incredibly strong, optimistic party," she said. "We feel very optimistic about our chances in the next election, and we are going to be working hard to come back to power."

MPs, senators vote for interim leader

Ambrose was chosen following voting under a preferential ballot process. MPs decided earlier in the day that Conservative senators could take part in the vote.

Conservative MPs and senators met behind closed doors Thursday to dissect the party's electoral loss and to map out a path to rebuilding the party.

The senators had lobbied to have some role in the selection of the interim leader. Under the Reform Act, a bill drafted by Conservative MP Michael Chong and passed last spring, the MPs could have voted to adopt a provision that only MPs vote for the interim leader.

As interim leader, Ambrose will not likely be eligible to run for the permanent job, but the rules around a leadership contest are not expected to come before January.

Former long-time Conservative cabinet minister Peter MacKay said Ambrose is intelligent and capable. Her conciliatory approach will serve the party, and Parliament, well.

"She has the ability to reach across the aisle on important issues and get things done and move these important files, having brought that experience to the fold," he told CBC News.

As for his own political plans, MacKay said his focus is on spending time with his young family in Nova Scotia. But he did not rule out a future leadership bid.

"You never say never, I learned that from Jean Charest a long time ago," he said. "Burning bridges and slamming doors is never a good career option ever."

Harper's new office on Parliament Hill will be the one used by former Liberal prime minister Paul Martin.

CBC News has also learned that the government provided the former prime minister with a ride home to Calgary on a Challenger jet.