Prime Minister Scott Morrison says his government will continue to function despite Hughes MP Craig Kelly moving to the crossbench after resigning from the Liberal party.
The shift to the crossbench puts the government into one seat majority, with 75 members of the House of Representatives plus control of the tiebreaking Speaker role.
After handing his resignation letter to Mr Morrison at Tuesday morning's Coalition party meeting, Mr Kelly told Sky News the decision was based on representing the views of his constituents in the seat of Hughes, in Sydney's south west.
"[It's] the best decision for myself and for the people I represent," Mr Kelly said from his parliament house office.
Nationals MP and former deputy prime minister Barnaby Joyce was seen in Mr Kelly's office following the party meeting.
The decision was announced just before Mr Morrison fronted a press conference, about raising the rate of the JobSeeker allowance
"As the government has led Australia through the worst situation we've seen since the World War II, we will continue to do so undistracted and we'll be able to do so with the support of the parliament from the very undertakings that the member for Hughes has indicated publicly," Mr Morrison said.
The Hughes MP has promised to support the government on all matters of supply or confidence.
In his letter of resignation, Mr Kelly acknowledged that some of his conduct over recent months "had not made the boat go faster."
Mr Kelly said he had the greatest respect for Mr Morrison and hoped his former party leader would go on to become one of Australia's longest serving prime ministers.
His decision to quit the Liberal party was a matter of representing his constituents.
"To be faithful to the oath that I took and to speak frankly and fearlessly I need to do that from the crossbench rather than from government benches," he said.
Mr Morrison told reporters he was also concerned about a staff member that remained employed in Mr Kelly's office after the MP was counselled about the staff member's behaviour. The staff member faced multiple claims of harassment against young women.
"I have long expressed to Mr Kelly my concerns about that staff member and he has long understood what my expectations were about how he would deal with that matter," Mr Morrison said.
Mr Kelly said he would continue to speak out about alternative coronavirus treatments.
"Being labelled an antivaxxer is a slanderous smear," Mr Kelly said. "I believe one of the greatest mistakes that's been made in this country and also the world was preventing doctors from prescribing [these treatments]. These other treatments should be used in concert with the vaccine."
Mr Kelly has shared coronavirus misinformation throughout the health crisis and had faced being disendorsed by the Liberal Party ahead of the next federal election.
Earlier this month Mr Morrison distanced himself from Mr Kelly over the issue.
It took months for Mr Morrison to make a public statement condemning the Hughes MP, who had been promoting two unapproved drugs on his Facebook page.
He has also long questioned the science behind climate change.
Mr Kelly threatened to quit the Liberals ahead of the 2019 election when he faced a challenge to his seat from within the NSW branch but was saved by Mr Morrison.
Senior Labor MP Linda Burney said Mr Kelly had been a "thorn in the side" of the Liberals for some time.
"The government has the slimmest of majorities in the parliament now," she said.