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The leader of Canada's federal Green Party, Elizabeth May, has stepped down.

She had held the role since 2006, and was the longest-serving of all major party leaders competing in last month's parliamentary election.

She was the only Green to hold a seat from 2011 to 2019. She was re-elected in the 21 October poll, and the party picked up two more seats in the House.

Ms May, who is 65, said she had promised her daughter that 2019 would be her last year as party leader.

"I absolutely swore to her 'last time, I promise'," she said, announcing her departure on Monday.

The Green Party attracted attention during the early stages of the election, as concerns about climate change grew. Although the Greens only got 7% of the popular vote, it tripled its seat count and Ms May said she feels the party is in a strong position to continue without her.

"We achieved more than one million votes for the first time ever," Ms May said. "I want to make sure that when I leave as leader of the Green Party we have momentum."

She said she would stay on as the leader of the party's parliamentary caucus.

Deputy leader Jo-Ann Roberts will be interim leader until the party holds a leadership contest in October 2020.

During the 2019 election, Ms May was the only female leader of a federal party.