May now faces uphill struggle of exerting influence on majority Conservative government, but she is in bullish mood

An American-born environmental lawyer, Elizabeth May, has been elected as Canada's first Green MP.

May, 56, and the leader of Canada's Green party, was elected on Monday night from a seaside community in British Columbia in an upset that unseated Conservative cabinet minister Gary Lunn.

Her win – in her third run as a Green candidate from three different provinces – gives the party its highest national profile yet in Canadian politics. Though a national leader, she was excluded from the televised election debates due to the lack of a parliamentary seat.

"Today we proved that Canadians want change in politics," she told a victory rally. "No one gave me very good chances of taking a seat from a cabinet minister when this began, but the enthusiasm of voters across this riding has just been spectacular."

May takes her seat in parliament under the first conservative majority government in years, and will struggle to exert influence on such combustible issues as climate change and development of the Alberta tar sands.

However, asked by the national broadcaster CBC what she could do as a lone MP, May said: "I don't even want to quote [former Canadian prime minister] Pierre Trudeau, but, 'Just watch me.'"

She said her first priority would be to raise the tone in parliament by campaigning against heckling during Question Period (Canada's version of prime minister's Questions).

The Green win was the result of a strategic shift by the party away from building broad-based national support to getting a foothold in parliament. After two failed runs in her home province of Nova Scotia and in Ontario, May moved to British Columbia in the summer of 2009 to focus full-time on her campaign.

While other national leaders fanned out across the country, she stayed close to home, campaigning in her Toyota Prius and mobilising an army of youthful volunteers to win over a conservative and elderly constituency.

The decision cost the Greens overall, with their share of the popular vote nationally falling to 4% on Monday night from 7% in earlier elections. It could also have left the Greens with nothing, had May failed to win the seat.

May, though born in Connecticut, was raised in Nova Scotia. Financial hardship forced her to drop out of college, but she was later admitted to do a law degree after receiving a recommendation from Bill Clinton. She began her career as an activist, campaigning against the use of aerial insecticides, before making her first run for office in 1980 for the Small Party at the age of 25.

She was elected the leader of the Green party five years ago on a promise to make the party a national force.