Green Party leader Elizabeth May failed in her bid to unseat Conservative Defense Minister Peter MacKay in Canadian elections Tuesday, dashing her party's best hope of getting its first MP into the House.

May lost by more than 5,000 votes in a campaign that saw her go head to head with the key cabinet minister, as the main opposition Liberals chose not to enter this particular race.

It was a "very satisfying, gratifying win," MacKay told broadcaster CTV.

But, "it created a different dynamic, to be sure, not having a Liberal candidate," he said.

"I think (it) disenfranchised a lot of people and we went out and ran an inclusive campaign, we reached out to people, including liberals, and we're very happy with the hard work that paid off tonight."

Under her new leadership, a party inextricably tied to environmentalism, once stagnating in obscurity, earning a mere 4.5 percent of votes in the last ballot by wooing disillusioned Canadians, doubled its support and vowed to elect its first MP in this election.

An environmentalist, writer, activist and lawyer, May entered the political fray after Conservative Stephen Harper was elected prime minister in 2006, she says, to "stop him at all costs," fearing his "dangerous" policies and his refusal to hear environmentalists.

This election, she explained, is the last chance to save a global climate change pact next year that Harper's administration has fiercely opposed.