Senator Jim Molan has died, aged 72, two years after he was diagnosed with an aggressive form of cancer.
In April 2021, he announced he was taking sick leave after being diagnosed with cancer.
He returned to parliament after his treatment and was re-elected to a six-year term in the Senate in the May 2022 election.
The Liberal Party will choose someone to fill his place until the end of his term in 2028.
Prime Minister Anthony Albanese described the late senator as "a man of principle and a politician of conviction".
"Jim Molan lived his life in service of our country," he tweeted.
Before entering politics, Senator Molan spent four decades in the Australian Army where he reached the rank of major general.
He served in Indonesia and East Timor, where he was awarded for his service, and went on to hold a senior operations role during the war in Iraq.
After retiring from the army in 2008, he became involved in politics in 2012.
His first taste of what would become his political career was working with former prime minister Tony Abbott's government on its policy to stop asylum seeker boats.
Operation Sovereign Borders became a controversial plan that turned back boats to Indonesia and saw Senator Molan work closely with former prime minister Scott Morrison.
Senator Molan is the father of Sky News presenter Erin Molan.
Colleagues pay tribute
Opposition leader Peter Dutton offered his condolences to Senator Molan's wife, Anne, and their four children.
"Jim was a distinguished soldier and military commander, an admired politician of centre-right convictions, and a perceptive author and respected public commentator who expressed his views with courage," he said in a statement.
"Whether it was on the battlefield, in the political arena, or on the media stage, Jim was admired for his discernment, leadership and unfailingly courteous manner."
Senator Molan entered the Senate in 2017 amid the dual citizenship saga, which cost Nationals senator Fiona Nash her seat.
He failed to get re-elected at the 2019 election but replaced Arthur Sinodinos in the Senate later that year.
Opposition Senate leader Simon Birmingham paid tribute to Senator Molan's ability to continue to work, despite his ill health.
"Even in the face of serious health challenges, Jim remained diligent in staying abreast of critical issues and determined in his pursuit of actions he believed were critical to Australia’s future security and prosperity," he said in a statement.
Senate leader Penny Wong said Senator Molan had been a "dedicated servant" of the people who, even through illness, had been a strong advocate for Australia's defence and national security.
"He was also highly respected for his contributions in other fields, including his Senate committee work on stillbirth," Senator Wong said in a statement.
