The National Legislative Assembly (NLA) overwhelming voted on Thursday to impeach former foreign minister Surapong Tovichakchaikul for reinstating the passports of former prime minister Thaksin Shinawatra.
The assembly voted 231-4 with three abstentions to impeach Mr Surapong. The NLA needed only 151 votes to ban him.
As a consequence, the former Pheu Thai Party MP is banned from politics for five years.
Mr Surapong is the fifth former Pheu Thai member impeached by the NLA, formed after the military coup in 2014. The number who voted to oust him was the largest of the five, including former prime minister Yingluck Shinawatra.
The former foreign minister is from Chiang Mai, the home province of the Shinawatra family.
The National Anti-Corruption Commission (NACC) submitted its resolution for his impeachment to the NLA last month, after a finding he that committed dereliction of duty under the Criminal Code in returning the passports to Thaksin in 2011, when he was the foreign minister. Thaksin's passports were revoked in 2008, two years after the previous military coup.
NACC member Supa Piyajitti reiterated the finding to NLA members at the start of the impeachment hearing, saying that Mr Surapong intentionally helped Thaksin, who at the time faced arrest warrants on several charges.
Mr Surapong argued that the NACC's accusation was groundless and the investigation finding should be annulled, alleging that one of the NACC members on the panel was not qualified to serve on it.
Authority to issue passports rested with the permanent secretary for foreign affairs, not the foreign minister, he added.