EDMONTON, Alberta — This is the Canadian province known for oil, cowboys and rodeos, and as the adopted home of Prime Minister Stephen Harper, whose Conservative Party has long dominated politics.

So it seemed especially jarring when a boisterous crowd in this bastion of conservative voting known as Canada’s Texas celebrated its new premier this weekend: a woman regarded by much of the country as a leftist who vows to take on big oil and champion the poor.

The 52 New Democratic Party members who sat behind the premier, Rachel Notley, their leader, in the swearing-in ceremony on Sunday did not resemble typical revolutionaries. Largely political novices, they dressed like junior bank managers. They include nurses, a phone technician and a yoga instructor.

The ceremony on the steps of the Alberta provincial legislature building, cheered by members of a large and enthusiastic crowd who could have easily passed for hockey fans celebrating a rare Edmonton Oilers victory, signified an exceptional moment in politics in both Alberta and Canada.