Sky Sports revealed on Tuesday that fresh terms were on the table and that an agreement was close.
The 22-year-old, who moved to Bournemouth from Brighton in 2011, will now stay at the Goldsands Stadium until the summer of 2016.
"The club is going places, I wanted to be part of that and I was more than happy to sign a new contract," he told the club's official website.
"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.
"Who knows where our future lies? But we've got a great set of lads and a very good manager and I think we will be successful."
Cook made 38 appearances last season as the Cherries secured promotion out of League One and scored his only goal in the last home game of the season against Carlisle.