The 18-year-old joins the Premier League newcomers on a four-year deal for an undisclosed fee.
Peart-Harris, as a product of Chelsea's youth rank never made a first team appearance for the Blues.
Brentford manager Thomas Frank told the club's official website:
“Myles is a very talented young player and an exciting signing for us.
“We see him playing as an ‘eight’ in our system and he fits the position profile perfectly for that. He is a dynamic midfield player, and he drives forward with the ball.
“Myles has great quality on the ball. He can score goals and deliver assists for us. He is great at arriving in the penalty area at the right time.
“There is also lots of development potential for our coaches to work with. We think there will be lots of areas where he will get better, particularly defensively, but he has some great attributes, and we believe we can maximise his potential.”
Peart-Harris becomes the eighth summer signing for Brentford as they gear up for their maiden season in the Premier League.
Co-director of football for Brentford Phil Giles stressed;
“Over recent seasons we have made sure we have found as many opportunities as possible to give young players a chance to play and develop.
“Even though we are now playing at a higher level, that principle is one we want to maintain. With that in mind we are looking forward to seeing Myles earn his opportunity and hopefully he can be another young player to make an impact at Brentford.”
