The Marin County panel found Max Wade, 19, guilty of commercial burglary and auto theft, after hearing evidence that Wade had rappelled into British Motors in 2011 to purloin the $200,000 convertible. The car was in the shop for repairs at the time.
Wade was also found guilty of attempted murder and firing a gun into an occupied vehicle in an unrelated drive-by shooting of a man who was dating a girl Wade desired. The man wasn't injured.
Marin County prosecutor Yvette Martinez said Wade had stolen the yellow Lamborghini to impress the girl and was willing to kill to get her attention.
Wade pleaded not guilty to all of the charges. He now faces up to 30 years in prison.
Detectives testified during the trial that they found the gun used in the shooting, two assault weapons and shotgun shells, as well as climbing gear.
Fieri, a star of Food Network, testified during the trial that he had never met Wade and never gave him permission to drive his car.
The teen made news again last year after at least two people tried to break into Marin County's juvenile hall with sledgehammers in an unsuccessful attempt to free him.
Authorities took extra measures to ensure security in the courtroom during the trial, keeping Wade tethered to a chair bolted to the floor.