The team includes Nauru's Electoral Commissioner Joseph Cain, Fiji's Supervisor of Elections Mohammed Saneem and a human rights lawyer from Swaziland Lomcebo Dlamini.
RNZI reports the Commonwealth Observer Group will be in Tonga from today until 20 November.
The election is being held next Thursday.
Official observers from the Pacific Islands Forum and the US Embassy in Suva will also be watching the election.
