The by-election came after Polanski faced criticism for his response to a motion passed by members declaring Zionism a form of racism.
Earlier, former party leader Caroline Lucas told the BBC Polanski had failed to show leadership over the motion.
Speaking after polls closed but before the result of the by-election was announced, Lucas criticised Polanski for not taking part in the debate or voting on the motion at the Green Party’s annual conference in Brighton on Sunday, describing the motion as “dangerous” and “divisive”.
Asked if Polanski should stand down, she said: “I think let’s just see what happens in the coming days and weeks. Obviously he has been completely taken up with this by-election.
“I want him to speak now about what’s happened, I want him to show the leadership that was frankly missing on Sunday.
“I think the jury is out about whether he will do that – but I very much hope he will.”
The motion defined Zionism as an ideology supporting “an ethnonationalist Jewish state” and backs a “single democratic Palestinian state in all of historic Palestine”, which includes modern-day Israel.
Polanski was not present for the vote on the motion, after leaving the conference early to campaign in Holborn and St Pancras.
