The Court of Disputed Returns in Papua New Guinea has ordered a by-election for the Gumine open electorate in Chimbu.
The court annulled last year's election win by Lucas Dekena on the grounds of illegal marking of ballot papers.
The petitioner in the dispute was runner-up Nick Kopia Kuman, who was beaten by 500 votes.
Mr Dekena is the third MP to be stripped of his election victory after Ezekiel Anisi and Paru Aihi.
A date for the Gumine by-election will be set by the Electoral Commission.