Greens senator Dorinda Cox has quit the minor party to join Labor in a shock defection less than a month after the federal election.

Cox announced her move to the government in Perth this afternoon alongside Prime Minister Anthony Albanese, saying it was the result of some “deep reflection”, but maintained she had campaigned loyally for the Greens for last month’s poll.

“It’s been over a period of time that I’ve considered this,” she said.

“It hasn’t, as I said, been a decision that I’ve made lightly. There are many conversations, many people that I sought counsel with across the political spectrum…

“So this wasn’t a decision that I did on the hop or based on emotion.”

Cox was the Greens’ spokesperson in a number of portfolios, including First Nations people, resources, and trade and tourism, and also was involved in selecting Larissa Waters as the minor party’s new leader.