Police said Parithat Poolphol, 45, managing director of Grand Eastern Co Ltd and Racing Spirit Co Ltd, shot himself with a 9mm pistol.
Police said he left a suicide note, saying he was under pressure because of his work.
He lived with his 20-year-old daughter. The daughter, who was in another room, heard the gunfire at 9.45am.
Racing Spirit has organised several racing events and is building a motor racing facility in Chon Buri with the budget of Bt4 billion.
It was later found that Parithat also recorded a clip on his cell phone talking about which of his assets would go to whom as an audio will.