Uri Warawara of the Graon mo Jastis Party won the recent by-election for the Malo Aore seat vacated when Havo Moli died in February.
Mr Warawara's victory gives the GJP eight MPs in the 52-seat parliament.
According to the Vanuatu parliament's official website, only the Union for Moderates has more MPs with nine.
The extraordinary session is expected to debate up to eleven bills including the Right to Information Act.
There are also amendments to the Penal Code, the Citizenship and Immigration Acts up for debate.
Photo: RNZI/ Walter Zweifel