The Election Commission has set the by-election date for Udonthani's 3rd constituency on Sunday, 30 August 2026, with candidate registration open for five days from 1 to 5 August.
On 24 July 2026, the Office of the Election Commission announced the Election Commission's declaration setting the election and candidate registration dates. This concerns the by-election for the Member of Parliament (MP) seat in Udonthani's 3rd constituency to fill a vacancy. Also announced was the Election Commission's declaration regarding candidate registration for the by-election in Udonthani's 3rd constituency following the royal decree calling for this election in 2026.
. Sunday, 30 August 2026, is designated as the election day. and Candidate registration will be held from 1 to 5 August 2026, between 08:30 and 16:30 each day. The venue for registration is the Phutthan Conference Room, 2nd floor, Phen District Office, Udonthani Province.
The 3rd constituency of Udonthani includes Phen District, Sangkhom District, and Ban Khao Subdistrict of Mueang Udonthani District.