Knott spent five years combined as part of the West Ham and Chelsea Academies, before he joined Sunderland in 2010.
The Essex-born winger made his professional debut for the Black Cats in a Premier League game against Tottenham in May 2013, following loan spells at AFC Wimbledon (January to May 2012), Woking (October 2012 to May 2013), Wycombe Wanderers (August 2013 to January 2014) and Port Vale (January to May 2014).
He joined the Bantams upon his release from the Stadium of Light in May 2014, and made 79 appearances in two seasons for the Yorkshire club. He scored eight times, including a memorable half-volley in City's League Cup victory over rivals Leeds United in August 2014.
Knott joined the Gills on a two-year deal in June 2016.