Crew extinguished the fire approximately three hours and 50mins into the flight, the airline says in a statement.The aircraft plane landed in Guam at 02:20 today.
There were 186 passengers, four infants, and 13 crew - nine cabin crew and four pilots - aboard the aircraft. The majority of passengers are Japanese, with a handful of other nationalities. There are no reports of injuries.
The fire occurred in the right-hand cockpit window area, leaving a blackened window.
Jetstar says it was caused by the electrical connector part of a cockpit window heater.
Among the youngest of Jetstar's six A330-200s, the aircraft joined the fleet in 2007. Its registration is VH-EBF.
After the aircraft landed without incident in Guam, the passengers "disembarked normally", a Jetstar spokeswoman says from Melbourne where the carrier is based. They are now staying hotels in Guam and waiting for another Jetstar A330-200 that has been dispatched from Sydney, she says.
The Australian Transport Safety Bureau (ATSB) says it has commenced an investigation. It also says it has notified the US National Transportation Safety Board and the France's Bureau d'Enquetes et d'Analyses (BEA).