The 22-year-old, who can play as a centre, wing or full-back, signed for the outfit four years ago and last season became top point scorer in the league.
"I have enjoyed my time at London Irish since joining the club back in 2008," said Homer. "It is a great environment to train in and I love playing at Madejski Stadium. There are definitely good times ahead."
London Irish director of rugby Brian Smith added: "Tom is a world-class footballer and a future England player. He has a big match temperament, an incredible boot and in my view is one of the most complete players in the Aviva Premiership.
"More important than all this is the fact that he's an outstanding character and a future leader at this club. You'll be hearing a lot more about Tommy Homer. He's destined for great things with London Irish and England."
Homer scored 278 points in the Premiership last season.