Elections have rarely been kind to Canada’s long-suffering Green party. Though many voters view it as the environmental conscience of the country, they often abandon it when it comes time to cast their ballot and the party’s leader, Elizabeth May, has sometimes been forced to fight for a place in debates between party leaders.

But as Canada confronts the effects of climate change, May and her party firmly believe October’s federal election will be different.

The Green’s growing strength was highlighted this week, when Paul Manly won a closely watched regional election in British Columbia, taking the Nanaimo seat from the leftwing New Democratic party, and forcing Justin Trudeau’s Liberal party into fourth place. He will become the federal Green party’s second MP.

May hailed Monday’s victory as “the dawn of a new era in federal politics” which proved voters were “brave to vote for real change”.

Manly’s win came soon after a provincial election in Prince Edward Island, where the Greens made Canadian history by becoming the official opposition for the first time by winning eight seats.

The recent successes come amid growing recognition of the impacts of climate change in Canada. A recent government report has found that the country is warming at a rate twice that of the global average.

Carbon taxes and environment have moved to the centre of the country’s national discourse, and May is well-positioned to capitalize on growing frustration among voters, said Lori Turnbull, a professor of political science at Dalhousie University.

“May can run circles around the [leaders] on the carbon tax. She’s really an excellent, speaker and debater and she’s got more experience than any of them in terms of running the federal party and being on the campaign trail,” said Turnbull.

The party’s recent successes have not come overnight.

May, who has led the party for the last 13 years, has worked hard to make Canadians comfortable with the prospects of Greens in parliament, crisscrossing the country to promote Green policies and meet with voters.

Such efforts may be enough to finally overcome voters’ tendency to abandon the party at the moment of voting: before elections, the Green party often polls around 8%, but their share has often dropped dramatically in final results.

The Greens’ recent successes could indicate that the party is finally becoming viewed as a credible alternative to more mainstream parties, rather than a “wasted” vote, said Turnbull. “They’ve been around long enough that it doesn’t feel like, ‘I’m throwing my vote to a party that’s not going to get anywhere,’” said Turnbull.

The party can also point to its commitment to running positive campaigns – differentiating its candidates from the mud-slinging of Canadian federal politics.

“Green support is far better established than I think people realize,” said Don Desserud, a professor of political science at the University of Prince Edward Island.

After studying the results of the Prince Edward Island election, he found that while the party won eight seats, it came second in 10 other races. “I wouldn’t ignore the idea that the Green party is starting to get some traction by having broadened their platform and presenting themselves as fiscally responsible party.”

Manly’s 12-point margin over the second-place Conservative candidate also highlighted the growing struggles of the leftwing NDP. The result marked the second loss of a seat for the NDP and its rookie leader, Jagmeet Singh.

The party has struggled to raise funds, and several high-profile NDP members will retire before the federal election, prompting speculation that disaffected NDP voters may defect to the Greens..

And while the Greens have little hope of winning the general election, the party is increasingly well-positioned to leapfrog the NDP as Canada’s strongest leftwing party – a potentially seismic change to the country’s political landscape.

Although Trudeau remains a popular figure on the international stage, recent polls show him struggling to win support at home; a handful of seats for the Greens could further empower the party in a minority government scenario.

“May is a formidable politician. She’s very experienced,” said Turnbull. “She’s very well regarded – and more people are going find it easier to cast a ballot for her.”

• This article was amended on 14 May 2019 to correct the spelling of Nanaimo.