Tei was found guilty of bribery during the campaign for Tonga's general election last November.
The ruling was handed down by Justice Laki Niu reports RNZ Pacific.
Last week successful election petitions were filed against the former prime minister, Pohiva Tu'i'onetoa and internal affairs minister, Sangstar Saulala, and both men were found guilty of bribing voters while campaigning for the election last year.
Tonga's finance minister Tatafu Moeaki was also found guilty of bribery.
They have now all lost their seats in Parliament.
All petitions were filed by members of Tonga's former ruling political party Patoa.
One against Minister Sangster Saulala was filed by rival candidate Piveni Piukala, who lost out in the contest for the Tongatapu number seven constituency.
It is unclear whether any of the former MPs are going to file appeals.
In total seven petitions were filed - four were successful and two were thrown out. One is still pending.
Tonga's parliament was supposed to sit on 16 May but it will now be postponed as a result of the latest ruling.
Photo file Screenshot Caption: DPM Poasi Tei at a press conference in April