The man who allegedly stabbed Mrs Smith has been named as Surasak Wannachot, 26, who is unemployed.
He was arrested in mountains in Nakhon Sri Thammarat Province today, police have announced, and will be brought to Phuket for questioning.
Meanwhile, police in Samut Sakhon province, to the west of Bangkok, have arrested the man believed to have driven the motorbike involved.
He has been named as Surin Tapthong, 46, who works as a motorbike tyre repairman in a shop on the bypass road.
Arrested at about 8am this morning, Surin is currently being ferried back under close guard to Phuket to face questioning and to be charged with his part in the killing.