Future Forward Party candidate Srinual Boonlue won the new election in constituency 8 of Chiang Mai on Sunday, beating a candidate from the Palang Pracharath Party by a comfortable margin.
Ms Srinual won the contest with 75,819 votes, followed by Nares Thamrongtipayakhun of Palang Pracharath with 27,781 votes, according to unofficial results.
The new election was called after Surapol Kietchaiyakorn, the winning candidate from the Pheu Thai Party, was disqualified by the Election Commission for breaching the election law by giving 2,000 baht and a clock to a monk before the general election on March 24. He claimed the money was for a merit-making ceremony on Feb 14, but the EC saw it as a political attempt to lure voters ahead of the poll.
In the March 24 poll, Mr Surapol, an eight-time MP in Chiang Mai, came first with 52,165 votes, followed by Mr Nares with 39,221 votes and Ms Srinual Boonlue with 29,556 votes.
As a new Pheu Thai candidate was forbidden from entering the contest, the party's supporters were believed to have switched their support to the Future Forward candidate as the two parties work together to prevent Prime Minister Prayut Chan-o-cha from holding onto power after the election.
The voting in Chiang Mai began at 8am and polls closed at 5pm.
