Lewis will join Falkirk after signing a one-year pre-contract agreement with the Scottish side.
Falkirk boss Paul Hartley is pleased to have added a player of Lewis' quality to his ranks.
He told the club website: “We are absolutely delighted to be able to secure the signing of a player of Dennon's calibre. He is an exciting, young talent who is extremely quick and I am certain that he is a player that will get the fans off their seats.
“Dennon is a player that has been on our radar for some time, he has proved highly sought after amongst clubs in the Championship and League One in England.
“We are thrilled to have been able to get him signed up and to have him with us for the start of pre-season."
Lewis, 21, will join up with Falkirk on July 1 ahead to their pre-season.