Planning Minister Richard Wynne has lost a high profile supporter as he battles to defend his inner city seat of Richmond from the Greens at the state election.

Barrister and asylum seeker advocate Julian Burnside QC, a long-time supporter of Mr Wynne, has defected to the Greens and written to Richmond residents calling on them to vote for the party's challenger in the seat Kathleen Maltzahn.

Julian Burnside, QC, a long-time supporter of Richard Wynne, has written to Richmond electors asking them to vote for the Greens' candidate. Credit:Alex Ellinghausen

Mr Burnside will not be voting for either candidate in Richmond, because he lives across the river in Hawthorn, but the Greens believe the barrister’s endorsement of their candidate will be a vote-winner in the seat where nearly three-quarters of first preference votes went left-of-centre in 2014.

The human rights activist told The Age that he had supported Mr Wynne in previous elections because of the minister’s record of advocating for asylum seekers.