The former Tory climate minister said the Greens had morphed into a toxic mix of “extreme left wing identity politics”.
It comes as the party investigates Leeds councillor Mothin Ali who shouted “Allahu Akbar!” after being elected and who has a history of inciting hostility against a Jewish rabbi.
Questions have also emerged about the party’s vetting processes as a number of councillors face allegations of antisemitism.
Lord Goldsmith told the Sun on Sunday: “Just as the environmental cause is going mainstream, the one party that actually exists to address it seems to have lost interest – and its mind.
“The Green Party has morphed into a toxic mix of authoritarianism, antisemitism and extreme leftwing identity politics.
“We saw that last week with the party’s blind embrace of radical Islamism, an ideology that tips easily into violence and which opposes precisely the kind of free, liberal and tolerant society the Greens are supposed to espouse.
“And we have seen it with the party’s unbending fixation with extreme trans ideology; a discredited and sinister cult that marginalises women and hooks countless confused and vulnerable children into a routine of lifelong medicalisation, mutilation, and very serious harm.”
In previous years former Green Party leader Caroline Lucas praised Lord Goldsmith’s “brilliant environmental work”.
But he said: “The tragedy is that we do need a strong Green Party while the mainstream parties get their act together.”
Green Party officials met with Lord Mann, the government’s independent adviser on antisemitism, this week to discuss the conduct of newly elected councillors.
Green Party co-leader Adrian Ramsay said while other parties were losing members “hand over fist”, they have been increasing their membership.
“We have attracted voters from all our diverse communities because we stand for protecting the environment, restoring public services and promoting peace around the world,” he said.
“I hope many more voters from all our diverse communities will be attracted to us at the coming General Election as a party that offers the hope and vision of a fairer, greener country.”