Wallace, 21, has featured 31 times for London Wasps but has decided to move to Bristol in order to maximise his game time opportunities.
London Wasps Director of Rugby Dai Young said: “There was a contract and a place in our squad next season for Jack but he goes with our best wishes and understanding as to why he wants to make the move. This is a mature decision from Jack who has a desire to keep progressing and get as much game time as possible."
"With the quality we have in our back three, the same opportunities to play as regularly as he would like are probably not available at the moment at Wasps and so I understand why he wants to go somewhere else right now. While we are disappointed always to lose a young player, I would like to think that Jack could always come back to us at Wasps in the future.”
Wallace added: "I've been at Wasps fulltime for four years and learned a lot in that time and really enjoyed it, but but right now I feel this is the right move for me. I want to keep progressing and push on as a player and that means I need to go somewhere to get more opportunities to play regularly."
"It is hard to leave Wasps. I have a lot of friends here and there are guys here around my age who I have come through the age groups with so it's not an easy decision. I have learned from some fantastic coaches and players at Wasps and I wish them all the best in the future. For me Bristol is an exciting move and I have been really impressed with their set-up and their vision. I am looking forward to the challenge."