The American-born 18-year-old is a product of the Ewood Park youth system and has become a regular this term under new boss Henning Berg.
Henley has been attracting glances from the Premier League, but Rovers have moved to tie down the Wales Under-21 international to a new contract.
Henley has penned a five-year deal with Rovers, despite having made just 15 appearances for the club.
He made his debut in the Premier League last year and only his second top-flight start came in their shock victory over Manchester United at Old Trafford on New Year's Eve.
"It is fantastic, it is something I've been working towards for a long time now and it feels great to get it done," he told the club's website.
"I really enjoy it here, I always have, I've been here since I was nine or ten and I've enjoyed every minute of it. It feels great to secure my time here."
And Rovers boss Berg added: "We are very happy that Adam has agreed to extend his contract. He is a talented young player, with good potential, who has done really well since he came back into the team.
"He has shown in the games that he is capable of doing well for us and we believe that this is the right place for him to develop further."
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