Justice Lesatele Rapi Va'ai, was sworn in before the head of state ahead of this week's hearings.
He has come out of retirement for 12 months to work alongside several other judges.
There are now 17 cases to be heard against decisions regarding around 200 candidates made by the Electoral Commissioner.
There cases were withdrawn.
They included a petition by Finance Minister, Sili Epa Tuioti, regarding a criminal conviction for one of his rivals.
