The 22-year-old, who joined the Dorset side from Brighton & Hove Albion in October 2011, played a major role in the Cherries' promotion last season, making 32 league starts.
"The club is going places," Cook told Brighton's official website. "I wanted to be part of that and I was more than happy to sign a new contract.
"I love the place. The lads here are brilliant and the gaffer has been a huge influence on me. As soon as a new deal was mentioned, I wanted to get it sorted.
"It will take me up to when I'm 25, so I'm sure a lot will happen in those three years because the club has come a long way even in the time I've been here."
Bournemouth will begin the new season with a home game against Charlton Athletic on August 3.