OUTGOING Australian Greens senator Bob Brown says his biggest political blunder almost saw him ban lesbian sex in Tasmania.

Senator Brown, who stepped down as party leader in April, said a tactical play in 1986, when the Tasmanian parliament was making the state's criminal code gender neutral, almost backfired spectacularly.

The 67-year-old's final speech to the National Press Club in Canberra today was littered with anecdotes about his political career, which ends in 10 days.

The story that got the most laughs related to his time campaigning for gay rights as a Tasmanian MP in the mid-1980s.

Senator Brown said he expected the then opposition Labor party to move to get rid of section 122 of the criminal code, which proscribed male homosexuality - but it didn't.

"So, very nervously, I moved that it also be made gender neutral and thereby (unwittingly) made lesbian activity illegal as well and the house immediately passed it," the former GP and conservationist said.

Senator Brown then rang a Liberal member of the state's upper house to say he'd made a "terrible mistake". He pleaded for his amendment to be overturned but was told it sounded reasonable.

However, as luck would have it, at the same time Queensland Premier Joh Bjelke-Petersen declared he wouldn't countenance banning lesbian sex.

Senator Brown sent a press clipping outlining Sir Joh's position to members of Tasmania's upper house "and they duly voted down this innovation that I'd sent them and saved my skin".

"So I'm grateful to Joh," he said.

The former Australian Greens leader will formally resign from the federal Senate on June 15 after 16 years in Canberra.

If all goes to plan, he'll be replaced by businessman Peter Whish-Wilson a week later.

Senator Brown's decision to leave without fanfare is in line with his declaration that he won't be writing a comprehensive autobiography.

"I prefer looking forward to looking back," he said.

Senator Brown sought to clarify, once and for all, his role in the death of rock legend Jimi Hendrix in London in September 1970.

Senator Brown was then a resident doctor at St Mary Abbot's hospital when Hendrix's body was brought in.

"He had been dead for some hours," Senator Brown said.

"He'd had a bit too much to drink and whatever else and had inhaled vomitus."

He said another Australian doctor signed the musician's death certificate while he went off to look after a patient who'd fallen under a train but was still alive.

He plans to set up the Bob Brown Foundation to foster environmental and green causes.

Originally published as Bob Brown 'almost banned lesbian sex'