The man, identified as 31-year-old Lachlan Jamws McGahey, was arrested by police on standard patrol at about 3:40am.
McGahey was found carrying what was described as a ‘Thai-made’ .38-calibre handgun, along with eight rounds of PMC-brand ammunition.
The eight rounds were loaded into the gun’s magazine.
Officers also seized a bullet holster and a black cloth pistol holster.
McGahey was arrested on the spot and taken to Patong Police Station.
He has been charged with possession of a firearm and ammunition without a permit, and carrying a firearm in a public area without a valid reason.
Legal proceedings are now underway, police reported.