The former party leader has been remembered as a giant of Australian politics, following his sudden death in Germany aged 74.
His family said they were devastated after he died on Sunday morning following an exercise session in Berlin, where he was part of an industry delegation.
"Simon was a fierce advocate for working Australians and dedicated his life to making a difference," the Crean family said in a statement.
Prime Minister Anthony Albanese said Mr Crean made a difference across a wide range of areas during his 23-year parliamentary career.
"He was a giant of the labour movement, to rise from being a union official right through to the ACTU presidency, and then to take the skills that he had into the federal parliament and to serve Australia," he told Seven's Sunrise program on Monday.
"He made a significant contribution across four different governments under Hawke, Keating, Rudd and Gillard, and he of course, then went on to lead the Labour Party.
"He was tireless, he was someone who has just been taken from us far too young."
Mr Crean followed in the footsteps of his father Frank, who served as treasurer in the Whitlam government and as deputy prime minister in the government's last months.
As ACTU vice-president, Mr Crean played a key role in bringing about The Accord between unions and employers in 1983.
Government Services Minister Bill Shorten said the news of Mr Crean's death was a terrible shock, paying tribute to his opposition to Australia's involvement in the Iraq War.
"If politics had a hall of fame, like some of our sporting codes do, Simon would be a member," he told ABC TV.
"To speak against the drums of war took real courage and then showing his consistency and integrity that once the troops were going he went down to farewell them along with (Prime Minister John) Howard."
Elected to the Victorian seat of Hotham In 1990, Mr Crean became science minister in the Hawke government.
Narrowly missing out on the Labor deputy leadership after Labor's election loss in 1996, he took on the position two years later after another election defeat.
After a third consecutive defeat in November 2001 he was elected unopposed as leader.
Mr Crean faced continued speculation about a Kim Beazley comeback amid poor opinion poll results and in November 2003 he resigned on the advice of colleagues - becoming the first Labor leader since 1916 to be replaced without having contested an election.
Former prime minister Julia Gillard said Mr Crean dedicated his life to Labor values.
"He hated injustice and fought hard to bring opportunity to all," she said in a statement.
"He took his work seriously but was also caring, sociable and fun."
Opposition Leader Peter Dutton said Mr Crean was a "gentleman".
"I always admired Simon for his intellect and decency ... A very sad day," he tweeted.
Home Affairs Minister Clare O'Neil, who replaced Mr Crean in the Victorian electorate of Hotham, said he was integral to events in politics and industrial relations for four decades.
"Every step of the way Simon backed me in my career and I saw him doing the same to so many other Labor women," she said.
Former prime minister Tony Abbott paid tribute to "a thoroughly admirable man".
"He never made the mistake of identifying the wellbeing of the country with his own personal advancement," he said in a statement.
After leaving politics Mr Crean continued to work for Australia's interests, most notably as chairman of the European Australian Business Council, Mr Albanese said.
Mr Albanese said the hearts of the Labor family went out to Mr Crean's beloved wife Carole, to his family and thousands of friends.
Mr Crean's family said his greatest achievements were as a father to Sarah and Emma and a loving husband to Carole in their 50-year marriage.
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