The 2019 Thai League 3 is the third season of the Thai League 3, the third-tier professional league for association football clubs in Thailand, since its establishment in 2017, also known as Omsin League Pro due to the sponsorship deal with Government Savings Bank (Omsin Bank).

Winners of third place play-off would promoted to 2020 Thai League 2.

This round was featured by Khon Kaen United, the first place of 2019 Thai League 3 Upper Region and Nakhon Pathom United, the first place of 2019 Thai League 3 Lower Region.

Both winners and runners-up would promoted to 2020 Thai League 2 automatically.

Khon Kaen United won 4–2 on aggregate.