Zack Polanski has been elected leader of the Green Party of England and Wales by a landslide, signalling a clear change of direction for the party.
The London Assembly member beat Green MPs Adrian Ramsay and Ellie Chowns, who were standing on a joint ticket, by 20,411 votes to 3,705.
In his victory speech, Polanski promised to build a “green left” to take on Labour, telling Sir Keir Starmer’s party: “We are here to replace you.”
His election potentially opens the door to electoral pacts with the new left-wing party being set up by former Labour leader Jeremy Corbyn and ex-Labour MP Zarah Sultana.
Polanski, a former actor who was the party’s deputy leader, campaigned on an “eco-populism” platform and has promised to make the party “bolder” and more radical in its approach.
In his victory speech, he said: “If you’re feeling hopeless, if you’re feeling in despair, if you’re feeling politically homeless, there is a political home for you.
“And I promise you, nothing will make you feel more inspired, more ready to get out there and more like we can turn our country around than joining the Green Party.”
He also took aim at Sir Keir, saying: “We will hold this Labour government to account.
“Because when we look at Keir Starmer and what this government have been doing, whether it’s the two-child benefit cap, the disability cuts, the genocide in Gaza, my message to Labour is very clear: we are not here to be disappointed by you, we are not here to be concerned by you, we’re here to replace you.”
The party said its membership had reached a record high of 68,500 during the leadership campaign, following an influx of new members.
During a sometimes fractious campaign, Ramsay and Chowns had accused Polanski of risking the party’s electoral gains with a “polarising, strident” approach.
Polanski paid tribute to his defeated rivals in his victory speech, and the other Green MPs, describing himself as “standing on the shoulders of giants”.
Unlike other parties, the Greens normally hold leadership elections every two years.
This year’s contest was due to have been held in 2024, after Ramsay and his co-leader Carla Denyer were elected for an extraordinary three-year term in 2021, but the poll was delayed in order to avoid a clash with the general election.
Denyer decided not to stand for re-election in May this year.
The Greens had record success at the General Election last summer, going from one to four seats in Parliament and overturning large Labour and Conservative majorities.
Together with the Scottish Greens and the Green Party of Northern Ireland, they won 6.7% of the vote.