A spokesperson for the Tonga pro-democracy movement says its members are delighted that legislation to ensure a more democratic parliament has been passed.
The new 26-seat parliament will include 17 MPs elected by the people, up from the current nine in a 30-seat legislature.
Ten of the seats will be for the main island of Tongatapu, which will be split into single-seat electorates, rather than the current multi-member seat.
Vava'u will have three MPs, up from the present two.
Ha'apai retains its two representatives and the two Niuas and 'Eua retain their single member seats.
A pro-democracy spokesperson, Po'i Pohiva, says the reforms are the culmination of two decades' work.
"This was one of the bases for the foundation of the movement - to bring about democratic life to Tonga and not only that to advocate and we have been doing that for the past two decades or so and we are very happy that we have finally come to this conclusion, this very important moment."