Adam Bandt will become the Australian Conservation Foundation's next CEO, officially abandoning further electoral pursuits with the Greens to take up the new role.
"It is a true privilege to help lead Australia's most respected voice for nature and climate at such a critical time," he said.
"Climate collapse is beginning, nature is in crisis and this is the parliament that can avoid extinction.
"We're setting politicians a test we hope they meet."
Mr Bandt's 15-year career in federal politics was cut short after the May election, when the size of Labor's landslide win, supported by a significant collapse in the coalition's vote, helped hand Labor candidate Sarah Witty a shock victory.
The Greens lost three lower house seats in the electoral massacre, leaving them without a leader and with just one representative in the House of Representatives.
In the aftermath, the minor party handed the reins to Queensland Senator Larissa Waters, who has welcomed her predecessor's move.
"It's a loss that we won't have Adam in the parliament, but I'm thrilled to see he will continue fighting for climate and nature," she said.
"I congratulate Adam and the ACF on this fantastic appointment."
Mr Bandt will formally step into the chief executive role in January, taking over from Kelly O'Shanassy after the foundation screened more than 300 candidates.
"Mr Bandt has the vision, the bravery and the experience required to meet the challenging years ahead as Australia grapples with devastating climate change and accelerating nature destruction," ACF board chair Ros Harvey said.
Some have blamed the Greens' losses on its departure from climate to other issues such as housing and the conflict in the Middle East, but the minor party has vowed to continue standing strong on social issues.
Mr Bandt led the Greens from 2020 until 2025.