A man arrested for allegedly assaulting police during the flag-burning melee at the "invasion day" march through Sydney is a Greens campaign manager who used to be a paid employee of the party.

Hayden Williams, 20, is also part of the anti-capitalist, anti-police, left-wing splinter faction in the NSW Greens, known as "Left Renewal", Fairfax Media can reveal.

He was arrested on Thursday and charged with assaulting police, resisting arrest and malicious damage. He has been bailed to appeal in Downing Centre local court on February 14.

In a statement, NSW Police said he was arrested during the anti-Australia Day march from Redfern after a "participant allegedly attempted to ignite a flag".