Alisdair Putt was acting as skipper of the four-man Aussie Old Salts team in the World's Toughest Row, a 4800km competition from the Canary Islands off Africa to Antigua in the Caribbean, when he suffered a suspected "cardiac-related event" on Thursday.
Race officials said Mr Putt was not able to be resuscitated despite the rest of the crew's efforts.
Mr Putt's family have been notified of his death.
"This tragedy will of course also have a profound impact on the other 37 teams we have still racing across the Atlantic," organisers said in a statement.
"The family of Alisdair have asked for understanding and support in respecting their privacy during this period of mourning.
"Our most sincere condolences are wholeheartedly offered to the families, friends and supporters of the Putt family, and the whole of the Aussie Old Salts team."
The Department of Foreign Affairs and Trade confirmed Mr Putt died near Sao Miguel Island in Portugal and a spokeswoman said consular assistance was being provided to his family.
"We send our deepest condolences to the family at this difficult time," she told AAP in a statement.
Mr Putt was a former agent with the Australian Security Intelligence Organisation, the national spy agency.
His current employment is listed as being a senior investigator with the United Nations International Residual Mechanism for Criminal Tribunals, according to his LinkedIn profile.
His past roles include immigration lawyer, war crimes investigator, reserve military lawyer and former Western Australian prosecutor.
Aussie Old Salts was the only Australian team competing in the gruelling event, and officials said the crew was put on a vessel headed for land.
Mr Putt was the oldest member of the crew, which also included Andreas Koenig, Stewart More and Alastair Horton.
The latter is a retired Australian special forces soldier who is not using his real name for security reasons.
Each of the crew was expected to row two hours on and off for 24 hours a day across the estimated six-week journey.
The team was fundraising for a local charity assisting Australian veterans transitioning to civilian life, as well as an Aboriginal women's and children's shelter in WA's Kimberley region.
In an interview with Nine newspapers in October 2022, Mr Putt expected to celebrate his 62nd birthday during the expedition and admitted he would be relying on the fitness of his slightly younger companions.
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