The 19-year-old left-back made his debut for the Bees in April and has made a total of five appearances.
"We are really pleased that Tom has committed this stage of his career to Brentford," head coach Dean Smith said.
"He has already shown great potential and we can help him become an established Championship player."
Brentford youngster Tom Field has signed a new contract, which will keep him at the Championship club until the summer of 2020.