The cabinet has approved a royal decree to hold a by-election in Constituency 9 in Bangkok which is expected to be held on Jan 30, according to Deputy Prime Minister Wissanu Krea-ngam.
The date is to be set officially when the decree is announced later. But the poll is expected on Jan 30.
The by-election is being called to fill a vacancy left by Sira Jenjaka who was disqualified as a ruling Palang Pracharath Party (PPRP) MP last week by the Constitutional Court.
Sira was convicted of fraud by the Pathumwan District Court in 1995 and sentenced to eight months in jail.
The term was halved because he confessed.
The ruling was prompted by a petition submitted by Seri Ruam Thai Party leader, Pol Gen Sereepisuth Temeeyaves. He had asked the court to rule on whether Sira was qualified to be an MP, pointing to his prior conviction.
Mr Wissanu said on Tuesday Sira must retroactively pay for the expenses for organising the last election in Constituency 9 while the Election Commission will cover the cost of the upcoming poll.
Traisuree Taisaranakul, a deputy government spokeswoman, said the royal decree is expected to take effect on Jan 2 and the registration of candidates to run from Jan 6-10.
Also on Tuesday, the Kla Party ("brave party") announced that its secretary-general Atavit Suwannapakdee will contest the by-election in a bid to reclaim his former turf.
Earlier, Pheu Thai leader Cholnan Srikaew said former candidate Surachart Thienthong, who remains active in the constituency, is expected to stand under his party's banner.
The Move Forward Party (MFP), meanwhile, has endorsed actor Karunpol Thiansuwan as its candidate in the by-election instead of former candidate Kritnucha Sansern, who finished third in the 2019 poll.
On Tuesday, the PPRP announced it will nominate Sira's wife, Saranrat, as the party's candidate in the by-election.
Mr Atavit said he would lead his team to the by-election with a firm commitment to the Kla Party's underlying principle of being a "doer", or pragmatic party.
This would teach his team of new-generation MP aspirants the trials and tribulations of an election, Mr Atavit said, adding he aimed to create a constructive political environment in Constituency 9 covering Laksi district. Mr Atavit formerly served as an MP in Chatuchak, Bang Sue and Laksi districts. In 2011, he won in Chatuchak district before losing in the 2019 general election.
He later left the Democrat Party and co-founded the Kla Party with Korn Chatikavanij, the former Democrat deputy leader and ex-finance minister.
Having served as an MP in Laksi district, Mr Atavit said he was well aware of residents' needs and has what it takes to reclaim his former constituency.
Democrat Party leader Jurin Laksanawisit, earlier told a party meeting the party would step aside for the PPRP, which previously held the seat, in keeping with etiquette.
Meanwhile, the cabinet on Tuesday approved changes to two organic laws governing the election of MPs and the other on political parties, essential for holding the next general election, deputy government spokeswoman Rachada Dhnadireks.
If they are given the green light by parliament, a dual ballot system will be in place to elect 400 constituency MPs and select 100 list MPs.