The 23-year-old’s new deal runs until the summer of 2031 and after featuring in every game for the Bees this season.
Frank said, "I'm very happy that we've agreed a new contract with Keane. He has been through a great development over the last couple of years.
"We know that he's an offensive player - a winger - mostly, but he can play all the front four roles; what he's also turned out to be is a very flexible and versatile player that can play multiple other positions, which he has shown this season by playing games at left-back, where he has done fantastically.
"For me, he is a fantastic Brentford player with a big skillset: one-on-one he is fantastic, his crossing is very good, and the way he helps the team is also so good.
"There is a big future for him here at Brentford."