His death was confirmed by his former Sodelpa party. Mr Qarase had been admitted to a Suva hospital two days ago.
The former civil servant turned politician led Fiji in the wake of George Speight's 2000 coup, and led Fiji through a tumultous period marked by broad economic liberalisation, marked by a series of constitutional controversies.
But after a lengthy and bitter falling out, then military commander Frank Bainimarama overthrew Mr Qarase in the 2006 coup.
Mr Qarase was jailed for a year in 2012 on abuse of office charges that stemmed from the 1990s, when he was the director of a number of companies and government entities. He denied the charges, maintaining they were politically motivated.
The Fiji government and Mr Bainimarama, who has remained prime minister since his coup, first through a period of military rule, then following elections, is yet to comment.