Death penalty
Thai newspapers say the teenager, whose name has been withheld, was arrested while trying to steer a cab backwards out of a Bangkok street with the driver still in the back seat.
Police claim the 18-year-old confessed to stealing the taxi and said he killed the 54-year-old driver after he fought back. The teenager could face the death penalty if he is found guilty.
Bangkok police Captain Veerarit Pipatanasak said: "He wanted to find out if it was as easy in real life to rob a taxi as it was in the game.
"He wanted money to play the game. His parents, who work as civil servants, did not have enough money to give him."
Thailand's Culture Ministry has recently been pushing for tougher regulation of games like Grand Theft Auto.
It wants stricter age ratings and restrictions on the hours that people can play games in arcades.
Ladda Thangsupachai, director of the ministry's Cultural Surveillance Centre, said: "This time-bomb has already exploded and the situation could get worse. Today it is a cab driver, but tomorrow it could be a video game shop owner."