The 20-year had signed a new contract last Christmas while on loan at Bury, but the club has moved to secure his services for the longer-term.
Tom has made seven appearances so far this season, having made his debut against Bradford City in the Carling Cup in August. He also scored his first goal for the club, against Hull City during the same month.
Having made over 100 appearances during loan spells at Accrington Stanley and Bury over the past two years, Tom returned to the club during the summer knowing it was a crucial year for him as a Leeds player.
"I'm delighted to be in this situation and I'm delighted to sign a new contract.
"I'm really chuffed with how things have gone so far. It's been tough, and I've been learning lots, but I've really enjoyed playing regularly and being a part of the first team.
"It's been a step up for me and it's a good challenge. I wouldn't have thought I would be in this position now, but I know my future is here and my aim is to keep improving, keep learning, and keep getting better."