Former NSW premier Bob Carr was the master of ceremonies at the state funeral for the passionate environmentalist on Wednesday at Sydney's historic Town Hall.

Mr Mundey died in May last year aged 90 but his memorial service was delayed because of the pandemic.

Mourners turned out in droves for the feisty radical, including his widow, Judy, NSW Governor Margaret Beazley, former governor Marie Bashir, NSW Labor leader Jodi McKay and Sydney Lord Mayor Clover Moore.

Mr Carr said "Australia's most famous communist" was best remembered for leading the green bans movement that preserved many of Sydney's heritage buildings but noted he also eventually became a Sydney City councillor, was on the Australian Conservation Foundation and chair of the NSW Historic Houses Trust.

The firebrand led the NSW Builders Labourers Federation during Sydney's construction boom in the 1970s, implementing 40 green bans - where unionists refused to work on projects - saving numerous heritage buildings from the bulldozers.

"What he was doing at that time was galvanising public opinion ... and laying the basis for heritage protection," Mr Carr said.

Never far from controversy, he took on powerful developers who under Liberal Premier Robert Askin "were levelling Sydney block by block" during a "feverish property boom" in the 1970s, he said.

"He stood with all of us in this hall today in seeing global warming as an existential threat," he said.

He was also remembered as a crusader for safety on building sites, an anti-Vietnam war campaigner, an advocate for feminism, gay rights and a passionate anti-apartheid campaigner.

Ms Moore said Sydneysiders owned Mr Mundey a huge debt for the preservation of the city's treasures including: The Rocks, Centennial Parklands, Pitt St Congregational Church and Kelly's bush.

Australian Associated Press