Kamikamica was rushed to hospital in March but held out hope that he could return to his club Melbourne Storm and lead Fiji at the World Cup in Australia, New Zealand and Papua New Guinea in October.
Instead he has hung up his boots on medical advice.
"I'm incredibly proud of everything I've been able to achieve in the game, representing Storm and captaining my country," he said in a statement.
"I'm so grateful to the club, my teammates, coaches, staff and everyone who has supported me and my family throughout my rugby league career."
Kamikamica played 142 NRL games, all for the Storm since his debut in 2017, including the 2024 and 2025 Grand Finals. He made 22 appearances for Fiji.
"He has been an outstanding player, teammate and leader, but above all else, Tui is a wonderful person who has always put his teammates and the club first," said Storm chief executive Justin Rodski.
Kamikamica was honoured by the club prior to the beginning of the Storm's Thursday night game at home to Penrith.
