The Seri Setia by-election is set to run concurrently with the Balakong state by-election on September 8, the Election Commission (EC) has announced.
Nominations and early voting for both Selangor legislative assembly by-elections are also slated to be held on the same day, which is Aug 18 and Sept 4 respectively.
This means all contesting parties would have an unprecedented 21-day campaign period for the two elections, despite both taking place in easily accessible urban areas.
Both Balakong and Seri Setia incumbents were from the Pakatan Harapan coalition.
The by-elections are the second and third respectively after the May 9 elections.