The cabinet on Tuesday approved a draft executive decree for the by-election in Ratchaburi province to replace sacked MP Pareena Kraikupt.
Deputy government spokeswoman Traisuree Taisaranakul said this clears the way for the Election Commission to set the date.
Deputy Prime Minister Wissanu Krea-ngam said after the meeting the poll could possibly be held on May 15, one week before the city elections in Bangkok and Pattaya. Elections for Bangkok and Pattaya city chiefs and councillors will be held on May 22.
The election will be held in constituency 3, which covers Chom Bung district and most of Photharam district.
The seat became vacant when Ms Pareena, of the ruling Palang Pracharath Party (PPRP), was banned from politics for life by the Supreme Court's criminal division for holders of political positions on Thursday for severe misconduct as an MP for her use of 665 rai of a forest reserve in Chom Bung for a poultry farm.
The by-election must be held within 45 days.
Deputy Prime Minister Prawit Wongsuwon, as PPRP leader, said the party already had a candidate for the seat, but refused to disclose the name.