Greens Senator Andrew Bartlett is stepping down to make way for Larissa Waters, who was booted from parliament last year over her dual citizenship.
Senator Bartlett will bow out in August to focus on running for the federal lower house seat of Brisbane at the next election.
"I'm wanting to give that election a red-hot go. It's a long shot but it's not an impossibility," Senator Bartlett told AAP on Saturday.
"Despite the huge importance of the Senate, winning House of Representatives seats is what really turbocharges change, and we sure as hell need a lot of change at the moment.
Ms Waters said she was delighted to be making a comeback.
"After six years in federal parliament and almost a year's break, I am more committed than ever to cleaning up politics and making it work for people and the planet, not corporate donors," she said.
"I've had a year watching politics from the outside, and it's clear that people are fed up with the big parties just doing the bidding of their corporate masters and donors."
