Ninkovich's agent, Craig Domann, tweeted that the deal includes $8.5 million guaranteed and total of more than $15 million.
"I'm happy to be here, I'm happy to stick around," Ninkovich said Monday in an interview on Boston sports radio station WEEI. "The Kraft family and my family worked it out to where it works well for both sides and I'm happy to be here for the next three, four years now."
In extending Ninkovich's deal, the Patriots re-upped their top pass rusher from last season and now have both he and Chandler Jones under contract through 2016.
Ninkovich, who had been playing in the final year of his current contract, said that the discussions on the new deal dated to training camp.
"In training camp I, obviously we were talking, I knew that I wanted to be here, this is the place I was given an opportunity and I really respected that because if it wasn't for the opportunity that was given here, I don't know where I would be right now," he said.
He said being with a strong organization trumped all in his mind.
"Given that, I really wanted to stick around and win games and be on a winning team," Ninkovich said. "That goes a long way as well. You can go search for money and all that stuff, but if you're losing every week, you'd be pretty miserable. I want to be here, I want to win and I want to help the team and just continue to be a good football player and be reliable."
A three-down player who seldom comes off the field, the 29-year-old Ninkovich has 14.5 sacks over the past two seasons, starting every game over that span. In addition to being one of the Patriots' top pass rushers, he is also considered a strong edge-setter in the running game and one of New England's most reliable players.
Ninkovich entered the NFL as a fifth-round draft choice of the New Orleans Saints in 2006. He joined the Patriots at the start of training camp in 2009 and was considered a longshot to earn a roster spot at the time, in part because he had been employed as a long snapper by the Saints at the time he was waived.
A knee injury in his rookie season stunted his development, but Ninkovich found his groove once joining the Patriots, elevating from backup and special teamer to front-line starter.