Tallis Obed Moses was installed as president by vote of the Electoral College, replacing Father Baldwin Lonsdale who died in office.
The opposition leader Ishmael Kalsakau said college members were lobbied to elect Mr Moses with the promise that the next head of state would be from Sanma province.
Mr Moses is from Malampa.
Mr Kalsakau said the promise eroded the democratic right of college members to vote for their preferred candidate from 16 people nominated for the role.
Photo file. Caption: Vanuatu President Tallis Obed Moses