Prime Minister Anthony Albanese says the Greens are “losing their way”, after the shock defection of a senator to Labor in the aftermath of the party’s tough election result.

Western Australian senator Dorinda Cox is quitting the Greens to sit with Labor in the upper house after approaching Albanese about making the switch.

Albanese said Cox’s values had become more aligned with those of his government, and noted the Greens had previously voted against Labor’s legislation to boost housing supply and had drifted from its environmental foundations to other issues.

“We know that the Greens have lost their way,” he told ABC radio on Tuesday.

“I think having to sit in the Senate while the Greens blocked funding for public housing would grate against anyone who regards themselves as progressive.”

Labor’s national executive will formally appoint Cox to the party on Tuesday, after the news was revealed on Monday.

The shock announcement represents another setback for the Greens, following the loss of former leader Adam Bandt, when three out of its four House of Representatives seats fell to Labor at the federal election.

Greens leader Larissa Waters said she had a “calm and measured” conversation with Cox an hour before the defecting senator stood up with Albanese to announce her decision.

“There’s no animosity there. It’s obviously disappointing for us to lose a Greens senator, but Dorinda has said her values lie there,” she told ABC radio.

But Waters appeared to question this while pointing to Labor’s decision to extend the North West Shelf gas project off the West Australian coast, which she said would impact ancient Indigenous rock art.

“We’ve opposed that. But Senator Cox has made her decision that that party is a better fit for her, and we wish her nothing but the best,” she said.

Asked about Cox becoming the second Indigenous woman to quit the Greens – after now-independent senator Lydia Thorpe – Waters said the pair had “very different reasons”.

Cox, a Yamatji-Noongar woman, became the Greens’ only First Nations representative when she joined the upper house in 2021 to fill a vacancy.

In 2024, as the party’s Indigenous affairs spokesperson, she suggested the Albanese government was “not interested” in closing the gap between Indigenous and non-Indigenous Australians.

But on Monday, Cox said she felt her values and priorities were better aligned with Labor than the Greens.

“I’ve worked hard to make Australia fairer and much more reconciled, but recently, I’ve lost some confidence in the capacity for the Greens to assist me in being able to progress this,” she said.

While she was not required to run in the May election after winning a six-year term in 2022, Cox reportedly had concerns about her likely position on the WA Greens senate ticket going into the 2028 poll.

Albanese said Cox, the first Indigenous woman to represent WA in the upper house, approached him about the switch.

Cox was accused of bullying Greens staffers in 2024, with as many as 20 employees leaving in three years and complaints made to parliament’s workplace support service.

Albanese said the allegations had been examined.

Labor will still require the support of either the Greens or the Coalition in the Senate to pass legislation.