Green Party London Assembly member Sian Berry has resigned her seat just three days after being re-elected.
The departure means that the Green Party's mayoral candidate, Zoe Garbett, will fill her place without a by-election.
Berry, who is running to replace Green MP Caroline Lucas as the MP for Brighton Pavilion, previously said she would "keep representing the people of London" until the general election.
Speaking to the Evening Standard, she also said she would only resign if she was elected as an MP.
Green Party London Assembly member Sian Berry has resigned her seat just three days after being re-elected
PA
Speaking on Tuesday, Berry said: "Zoë has shown how much of a difference she will make in City Hall, listening to Londoners and bringing their voices into the political debate.
“That’s why she needs to be in this job as soon as possible.
"She is already a brilliant councillor and will be a brilliant assembly member for Londoners.”
Berry has served on the London Assembly since her election in 2016.
She also stood as the mayoral candidate for the Green Party in 2008, 2016 and 2021.
Berry was re-elected as a London-wide assembly member on Saturday.
Following her decision to resign, Garbett said: "I am excited to join the Assembly and get to work for Londoners.
"There is so much to do to improve the quality of our lives in London, stand up for people on the margins and hold the mayor to account."
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Garbett, who stood as a candidate in the London mayoral elections last week, recieved 5.8 per cent of the vote putting the Green Party in fourth place.
The party came third in the previous three mayoral elections.