Bertrand began his youth career at Gillingham, before signing for Chelsea in July 2005. He graduated from Chelsea's youth system and was sent on loan to various clubs between 2006 and 2010. He made his full debut for Chelsea on in April 2011, six years after joining them, in a fixture against Birmingham City. In the 2011–12 season, Bertrand signed a new four-year contract with Chelsea and was made understudy to Ashley Cole. In May 2012, Bertrand became the first player to make his Champions League debut in the final, starting in an unfamiliar left wing role in front of Cole; Chelsea beat Bayern Munich 4–3 on penalties.