The 21-year-old right-back is now tied to the Premier League club until the summer of 2032, with an option to extend for a further year.
Kayode earned a Premier League Young Player of the Season nomination after an outstanding 2025/26 campaign.
Since arriving from Fiorentina on an initial loan deal in January 2025, he has made 56 appearances in all competitions for the Bees.
"Michael had an amazing season last year,” manager Keith Andrews told club media.
"He epitomised everything good that we do. His development and evolution has been really, really impressive.
"Michael’s someone that we love working with every single day, who comes in with such an enthusiastic demeanour, and is a joy to be around and to coach.
"We’re absolutely delighted that he wants to stay because we love having him here, and this new contract is absolutely deserved."