Stephen Harper was upbeat in the face of a one-sided election defeat, but will step down as Conservative leader following the result.

Conservative Party president John Walsh released a short statement shortly before Harper took the stage in Calgary, indicating Harper had instructed him to reach out to the elected caucus to appoint an interim leader and begin the next leadership selection process. The party is expected to issue a further statement on that process Tuesday morning.

Harper, who was seeking a fourth consecutive term as prime minister since 2006, enthusiastically greeted supporters before taking the podium in "our home, our Calgary" for his concession speech.

Harper did not mention his political future in his speech. He said he had spoken to and congratulated Justin Trudeau, the fourth Liberal leader he has faced in a federal election.

The Conservative leader said it was an electoral result he would "accept without hesitation," and he pledged to help Trudeau with the transition of power.

Harper had led the party to increases in seat totals in three consecutive elections. But in this marathon campaign, the party's attempt to paint Trudeau as too inexperienced for the highest office in the land proved unsuccessful.

Harper has spent over nine years in power and 13 years as a party leader, having officially become leader of the Opposition as Alliance leader in May 2002.

'We put everything on the table'

Harper, 56, called it "an incredible honour" to serve as prime minister of the country.

"We put everything on the table, we gave everything we have to give, and we have no regrets whatsoever," he said of the 78-day campaign.

"The disappointment you also feel is my responsibility and mine only," he told supporters.

Harper thanked his wife, Laureen, and teen children, Ben and Rachel, who were in elementary school when he was first sworn in as prime minister in 2006, for their support in "making everything possible."

Stephen-Laureen-Harper

Stephen Harper and his wife, Laureen, greet supporters in the Calgary Heritage riding prior to the Conservative leader conceding defeat. (Jeff McIntosh/Canadian Press)

Harper heralded his government's accomplishments over the years, including its fiscal management of the country, job creation, a variety of trade agreements Canada has struck with partners around the globe and a strengthening of the Canadian Forces.

The Conservatives won 166 seats in the 2011 election, their only majority with Harper at the helm, but were poised to lose dozens of seats as of early Tuesday.

Harper, who in previous election night speeches promised to unite Canada and lead an inclusive government, was accused of divisiveness during the campaign due to the party's slow and inconsistent response to the Syrian refugee crisis and their ongoing court battle over the wearing of the niqab at citizenship ceremonies.

Alberta was a beach head for the party, however. Health Minister Rona Ambrose and Defence Minister Jason Kenney won their seats, while other members of Harper's cabinet — Michelle Rempel, Kevin Sorenson, Deepak Obhrai — were re-elected.

Northeastern B.C., and southern Saskatchewan also went heavily blue, but east of southern Manitoba, there was little for the Conservatives to cheer about.

The Conservative leader had told Peter Mansbridge of CBC's The National during the campaign that he had no intention of trying to form a coalition if his party didn't finish first in seats.

"My position has always been if we win the most seats, I will expect to form the government and if we don't, I won't," he said.

Forming the Opposition

Harper in his concession speech pledged to help his party become an effective force as the Opposition and to prepare it for the next federal election.

"When the next time comes, this party will offer Canada a strong and clear alternative, based on our Conservative values," he said.

Harper comfortably won his Calgary Heritage riding and will continue to serve as MP in the immediate future, The Canadian Press reported. He received over 63 per cent of the vote with over 80 per cent of polls reported.

"This is the seventh mandate you've given me, and it remains a true privilege to serve this vibrant city in the Parliament of Canada," he told his local supporters.

Harper exited the stage as Collective Soul's Better Now blared in the background.

A campaign official told CBC News that Harper didn't mention the party's imminent leadership process because he wanted to focus on Conservative accomplishments in his speech, and not his individual future.

It was Harper's fifth federal election, his first loss since he tried to unseat Liberal Leader Paul Martin in 2004.

Harper won the leadership contest for the Conservative Party which resulted in 2004 from the merger of the Alliance and the remnants of the struggling Progressive Conservative Party.

With files from The Canadian Press