Australian Foreign Minister Alexander Downer told the Australian newspaper that Fijian leader Commodore Frank Bainimarama made the commitment at the South Pacific Islands Forum, currently in session in Tonga.
The coup leader, who toppled Fiji's elected government last December, had previously only agreed "in principle" to return the country to democracy.
Downer, who is attending the forum in Tonga, said that sanctions on Fiji would be reviewed once clear progress had been made toward elections.
Leaders of the 16-member forum retreated to the Tongan island of Vava'u for the second day of deliberations.
New Zealand Prime Minister Helen Clark said Bainimarama's pledge was a "very good outcome" for the forum as "the leaders would not have settled for anything less than an absolute acceptance of a timetable for elections no later than the first quarter of 2009."
Clark said sanctions against Fiji "do appear to be working" as economic growth, which had been running at 2 percent had fallen to minus 3.1 percent.