OTTAWA — With an economy dominated by the oil industry and a conservative, free-market political tradition, Alberta has long been cast as the Texas of Canada. But on Tuesday, not only did the province’s voters put the Progressive Conservative Party out of power after 43 years, they elected a government from the far left of Canada’s mainstream political spectrum.

The unexpected rise of the New Democratic Party, which was partly founded by labor unions, may have implications for Alberta’s oil sands, which, many critics say, enjoyed a light regulatory touch under Conservative governments. And with a federal election coming this year, the result will not be welcomed by Prime Minister Stephen Harper, a Conservative whose party’s power base is in Alberta, along with his own parliamentary constituency.

The New Democrats had always been distant also-rans in Alberta, Canada’s most conservative province, so there was skepticism before the election about polls that showed the party far ahead. But broadcasters declared about an hour after the polls closed that the party, under its leader Rachel Notley, had won a strong majority of seats in the provincial legislature.

Preliminary results indicated that the New Democrats would have 53 seats, up from four, while the Conservatives would fall to third place, with 11 seats, behind the Wildrose Party, another right-of-center group, with 21.