Victorian Labor senator Kimberley Kitching has died suddenly in the Melbourne suburb of Strathmore.
The ABC understands Senator Kitching, 52, died of a suspected heart attack on Thursday afternoon.
She began feeling unwell while driving between two meetings and pulled over before calling her husband, Andrew Landeryou.
An ambulance was called but she could not be resuscitated and died near to where her vehicle was parked.
Labor leader Anthony Albanese said the party was "in shock" over her sudden death and she would be "deeply missed by us all".
"All of us in the Labor family are in shock tonight at the sudden death of our friend and colleague, senator Kimberley Kitching," Mr Albanese said.
"Kimberley gave so much. She had so very much ahead of her.
"Kimberley had such a larger-than-life personality that it is tragic that her bright light has gone out far too early.
"Our thoughts now are now with her family and all who loved her, especially her husband Andrew."
Prime Minister Scott Morrison said Senator Kitching was "a parliamentarian in the truest sense" and "deeply respected by the Coalition".
"She demonstrated that her passion for her country was always greater than any partisan view," he said.
"She clearly loved her country and it genuinely showed."
Deputy Labor leader Richard Marles said: "Nothing can describe the shock and sadness of this news."
"I have known Kimberley as a friend for over 30 years. Words cannot express the sadness of this moment," he said.
Former Labor leader Bill Shorten said Senator Kitching's passing was "an immense loss to Labor and the nation".
"To know Kimberley was to be touched, not just by her serene intellect, but her incredible warmth and vivacity," Mr Shorten said in a statement.
"As a Labor senator she was relentlessly energetic and conscientious, recently resulting in international recognition for her human rights work.
"As well as her innumerable accolades she has been a wonderful friend to myself, my wife Chloe, and our family."
Preselection stress
Several of Senator Kitching's colleagues said an ALP preselection challenge had recently caused her considerable stress.
Senior figures of the Victorian Right of the ALP – Senator Kitching's faction – held a Zoom call on Tuesday night and it is understood her preselection was a "discussion point".
The ABC has been told that when challenged, neither Sam Rae, the former state secretary of the ALP and now the preselected candidate for the seat of Hawke, nor Michael Donovan, the Victorian secretary of the Shop, Distributive and Allied Employees' Association, would endorse Senator Kitching's preselection.
"Kimberley was stressed by all this bullshit," one Labor member told the ABC.
"Some in the party were trying it on.
"She and Kim Carr are the only ones in Labor who haven't been preselected.
"And this close to an election, it was a try-on.
"Those playing games didn't even have another candidate to replace her."
Several of her colleagues told the ABC that Senator Kitching, a feisty figure both within her party and inside parliament, had lost considerable weight due to a strict diet. Her death came less than a week after Shane Warne's, he was also 52.
"She had trimmed down," one of her parliamentary colleagues said.
'Everyday Australian people'
Senator Kitching was born in Brisbane before moving to Melbourne in 1995.
During the 2013 federal election, she made a bid for Labor preselection for the Victorian electorates of Lalor and Gellibrand, but was unsuccessful.
Three years later, in 2016, Senator Kitching won preselection to fill the Victorian Senate seat vacated by Stephen Conroy's resignation.
In her maiden speech to parliament, Senator Kitching said: "As a former Queenslander who grew up swimming, a proud holder of a bronze medallion, who continues to enjoy swimming in Victoria's chillier waters, I am daunted yet delighted to be thrown in the deep end right here and now."
"I am mindful and deeply humbled that only 591 Australians have ever served in the Senate," she said.
"I come here to represent everyday Australian people."
During her time in politics, Senator Kitching pursued her passion of human rights and was a key figure in the push for the Magnitsky Act.
The laws allow for travel bans and the seizure of assets belonging to foreign nationals who have violated human rights.
They have recently been used by the federal government in response to Russia's invasion of Ukraine.
The head of the Global Magnitsky Justice Campaign, Bill Browder, said he was deeply saddened by the death of his friend and ally.
"She was the driving force behind the Magnitsky Act in Australia, a true advocate of the victims of human rights abuse and one of the nicest people I've ever met," he said on Twitter.
