The National Championship was the next stage from the regional stage of

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. The winners and runners-ups of each region would qualify for this round to find 3 clubs promoting to

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Teams

Group stage

Upper region

---- ---- ---- ----

Lower region

---- ---- ---- ----

Knockout stage

Winners, runners-up, and third place of

would be promoted to the

Third place play-off

Summary

Matches

''Nakhon Si United won 4–3 on aggregate.''

Final

Summary

Matches

=1st leg

= ----

=2nd leg

= ''Uthai Thani won 3–1 on aggregate.''

Statistics

Goalscorers

Teams promoted to 2022–23 Thai League 2

:* Uthai Thani (champions) :*

Krabi Krabi (, ) is the capital of and main town in Krabi Province (''thesaban mueang''), on the west coast of southern Thailand, where the Krabi River flows into Phang Nga Bay. The town lies south of Bangkok, and as of 2020, has a population of 32, ...

(runners-up) :* Nakhon Si United (third-placed)

References

{{DEFAULTSORT:2021-22 Thai League 3 National Championship Thai League 3 3