Patrick Lagrou, 55, was arrested in Phuket on Saturday night by immigration police led by Pol Col Sanchai Chokkhayaikij, the Phuket immigration police chief.
Pol Col Sanchai said Mr Lagrou was wanted in Belgium for growing marijuana and was found to have accumulated wealth of about 25 milllion euros (about B1 billion) from trade in contraband.
He escaped arrest in Belgium and fled to Thailand, leading to his being apprehended in Phuket at the request of the Belgian authorities.
Mr Lagrou is being detained for further legal proceedings.