The South Australian's death was announced in parliament on Monday, with the Senate suspended as a mark of respect.

Opposition Leader Anthony Albanese said the former truck driver and labourer rose through the ranks as a union official before entering parliament 10 years ago.

"Alex's career was indeed a fine one. We in Labor are very proud of Alex. He was a conscientious, no-nonsense man," he said.

Prime Minister Scott Morrison described Senator Gallacher as a servant of Australia who loved the Labor Party.

"May God bless him," he said.

"May our colleague and friend rest in peace."

Born in Scotland, Senator Gallacher worked in transport and aviation before becoming an official and state secretary of the Transport Workers' Union.

He was elected in 2010 and took his seat in the upper house in July the following year.

In a statement, Senator Gallacher's family said he battled with courage until the end after his December 2019 diagnosis.

"It is with great sadness that our loving father, husband, brother and grandfather, senator Alex Gallacher, passed away peacefully on 29 August 2021," the family said.

"Our family takes great comfort and pride that his legacy in the Senate has in some way contributed to the progress of our nation."

Labor's Senate leader and fellow South Australian Penny Wong said he remained dedicated to his work despite his deteriorating health.

"Alex's fragile health as a consequence of his cancer diagnosis was widely known. However, this does not make the news of his passing any easier," she said.

During his time in parliament, he was took leading roles in foreign affairs and economics committees, and was a long-time member of the rural affairs and transport committee.

Government upper house leader Simon Birmingham said Senator Gallacher was a staunch advocate for road safety and aviation workers.

"A straight shooter, you always knew what Alex believed and where he stood," the SA Liberal said.

"Despite his cancer diagnosis in December 2019, Alex continued to represent the people of South Australia, the Labor Party, the trade union movement and his constituents with diligence and passion."

Australian Associated Press