Greens Sarah Hanson-Young and Mehreen Faruqi look set to face off for the party’s leadership, with the pair both promising to bring the fight to Labor and One Nation after Larissa Waters’ shock resignation.

Hanson-Young confirmed on social media she was discussing a tilt at the leadership with colleagues on Tuesday, ahead of a two-day party retreat in Sydney, when the new leader will be chosen.

Faruqi said she would run on a joint ticket, with the Tasmanian senator Nick McKim as her deputy.

The contest will see Hanson-Young, the party’s longest-serving and best-known senator, up against Faruqi, the current deputy leader.

“I am speaking with my colleagues about the best way to help the Greens and have asked for their support to be the next leader,” Hanson-Young said in a statement.

“People deserve better than the failed policies and weak excuses from the Labor and Liberal parties and the hate peddling from Pauline Hanson’s One Nation.

“Our communities and environment are being hammered by a rigged system and they want politicians that will fight for them.

“I will fight with everything I’ve got.”

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Faruqi and McKim said in a joint statement that the party needed to grow.

“We need to take the fight to Labor and a broken economic system that rips off young people, keeps working people drowning in bills and wreaks havoc on nature and climate,” they said.

“As the far-right gains strength, we think we are the right people to resist, and to grow our movement alongside our colleagues, members and supporters. Our politics are unapologetically bold and we want to lead with hope over hate and people over profit.”

Party sources said Greens MPs were blindsided on Monday when Waters revealed she would quit the leadership to focus on treatment for kidney disease, after her health had declined significantly since being elected leader in May last year.

Hanson-Young has previously sought the party’s leadership but been rebuffed by colleagues.

Greens senator David Shoebridge. Photograph: Mick Tsikas/AAP

All positions will be declared vacant and negotiations could be held to avoid a ballot in the 11-person party room. A retreat to discuss policy and strategy had been planned before Waters quit, with the leadership question expected to be resolved by Thursday at the latest.

The New South Wales senator David Shoebridge refused to comment on a possible tilt at the leadership on Tuesday.

He praised Waters for her bravery and called for the Greens to remain the “progressive party of choice”.

“I’m not here to rule anything in or anything out in terms of leadership,” he said. “That will be a matter … that the party room makes a decision on.”

Guardian Australia has been told negotiations could also include possible candidates for the deputy leadership, including Victorian Steph Hodgins-May and Queenslander Penny Allman-Payne.

The former Greens MP Max Chandler-Mather on Tuesday called for the party’s membership to get a vote in the leadership race.

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Defeated at last year’s election, the former Griffith MP is now the head of the party thinktank, The Green Institute.

A party plebiscite in 2020 saw 62% of Greens members support a rank and file vote for leader, but the move fell short of a required two-thirds majority.

“People often ask how to recreate the political success and energy of UK Greens leader, Zack Polanski, or New York mayor, Zohran Mamdani,” Chandler-Mather said.

“The recipe for their success doesn’t just lie in their policies, rhetoric or even organising strategy. It lies in the process by which they won their elections. In both instances they were elected by direct member elections.

“If we want to win real change, then the Greens should aspire to become a genuine mass membership party with well over 500,000 members, where its support and organisation reaches into the working class communities long abandoned by the Labor party.”

The party’s new leader will come under pressure to bring a more forceful approach to the job, amid frustrations that Waters’ more moderate style has stopped the party from exploiting a move by voters away from Labor and the Coalition.

The former leader Adam Bandt, Chandler-Mather and MP Stephen Bates all lost their seats at the 2025 election, and One Nation has replaced the Greens as the third major force in federal politics.

In a letter to party members, Waters said she was sad that illness had “cut my time as leader short”. She talked up success in negotiations with Labor on environmental laws and the response to the Bondi beach terror attack.

“But our Greens movement is too important, and I want to pass the torch over to someone who is ready to take up the fight,” she said.

“In the face of shifting political sands ever since, we have been the only party to hold – and grow – our support in the polls against the rightwing surge.”

Waters will take medical leave before returning to the Senate.

The prime minister, Anthony Albanese, wished Waters well, and praised her constructive approach on Senate negotiations.

“When I spoke to her, she was going off to see further health checks today. And I wish her well,” he said.

“This is a job, and a leadership position for a minor party means a lot of travel and a lot of pressure … she wasn’t in a position to be able to do that job going forward. But she intends to stay in the Senate.”