David Coon won the hotly contested Fredericton South riding in the New Brunswick election on Monday, beating the province's energy minister. It's the first-ever seat in the province's legislature for the Greens.
"Today is a happy day for Greens," May, the leader of the federal party, said Tuesday in an interview with The Canadian Press.
"We have now the clear indication that Green votes are not restricted to British Columbia ... a clear indication that what we have as a message resonates with people."
May went so far as to suggest that in the event of a minority government in 2015, the federal Greens could be elected in sufficient numbers to hold the balance of power.
"We're very hopeful that in the next election campaign that I will be in a leader's debate, that we will be in a position to have Greens elected in sufficient numbers to potentially be the balance of power that David Coon almost was last night."
Currently only May and Bruce Hyer, the former NDP MP from Thunder Bay who switched to the Greens late last year, sit as party members in the House of Commons.
May pointed to the influence of the Greens in Australia, saying a small Green cohort helped push forward climate legislation there.
She said if Canada's Greens find themselves in a similar situation following a federal election next year — and are in talks with a minority government — they would demand action on climate, reform of the electoral system and proportional representation.
"We are running out of time on climate; it is non-negotiable," May said. "And I don't trust any of the other parties to actually understand what needs to be done unless we're there to ensure that they do."
May also suggested her party has more of a conscience than the NDP.
"On principle, on a range of issues, we're the voice of conscience," she said, pointing out that she was the only MP to vote in 2011 against a continuation of aerial bombing in Libya after there was a ceasefire proposal on the table.
"I was really shocked to be the only one," she said, adding she voted against continued bombing due to concerns for the civilian population.
"And I know for a lot of NDP voters who had been peace activists for years — that's when they decided to shift to the Greens. They couldn't believe it."