Harper, in power since 2006, dissolved parliament after meeting with Governor General David Johnston, the representative of Queen Elizabeth II, Canada's nominal head of state in this Commonwealth country.
Voters will be choosing all 338 members of the House of Commons, 30 more than in the last election because of redistricting.
Harper said the election was about "leadership on the big issues that affect us all, our economy and our nation's security."
"It's an election about who will protect our economy in instability and ensure Canada's future prosperity. The national election is not a popularity contest," he added.
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Harper had planned to present himself as one of the first G7 leaders to post a balanced budget since the global financial crisis, bolstering his image as a strong fiscal manager.
But that was dinged by massive job losses and lower royalties due to a drop in oil prices over the past year, and growing uncertainty about Canada's economic future.
Boosting national security is also likely to factor into campaigns, after attacks on Canadian soil last October.
But instead he has reaped scorn for dramatically expanding the powers and reach of Canada's spy agency in the biggest overhaul of the nation's anti-terrorism legislation since 2001.
"This election is also about security," he said.
He added that Canada must confront "the violent global jihadist movement that possesses a direct threat to our friends, allies and to us here at home."
Trudeau will try to lead the Liberals back into power for the first time since ceding power to the Conservatives in 2006.