The pair, who will work across all of the agency's accounts, join from the LBi Group, where they were a senior creative team.
They were most recently involved in creating thisisliving.tv, the digital component of the European launch campaign for the PlayStation 3.
Gary Hoff, the iChameleon creative director, said: "Paul and Tim have a great breadth of work and we hit it off with them from the start. I'm expecting great things for them and they will add some serious weight to the creative team."
Before joining LBi in 2006, Knott was a creative group head at Modem Media, working on the BT account. Vance joined the agency in the same year from Tribal DDB.
While at LBi, the pair picked up awards at Cannes, D&AD and the One Show for their work on the Volkswagen Phaeton and Kendall Tarrant's "Interviews from Hell".
IChameleon has further boosted its team with the appointment of two graduates, Stuart Woodall and Sean Vrabel, from Lincoln College.
Hoff said: "Stu and Sean have had a great internship here and are now working on some fantastic projects. Taking them on full time was the obvious next step."