When defensive end Chris Long got a four-year extension on the first day of training camp, the team said Laurinaitis was also a priority. The Rams announced the deal on their Twitter feed Saturday, saying the team was "thrilled to announce" the signing.
The extension, which runs through the 2017 season, is worth $41.5 million and includes guarantees that total more than $23.5 million, a league source told ESPN NFL Insider Adam Schefter. The deal could be worth as much as $44 million for Laurinaitis, the source said.
Laurinaitis, a second-round pick in 2009 out of Ohio State, has led the Rams in tackles all three of his seasons, with double-digit totals every year. He's been durable, too, starting every game.
He has five career sacks and three interceptions.
"I've learned a lot, played a lot," Laurinaitis said during training camp. "Every year I've just tried to get a little bit better, make fewer and fewer mistakes and be accountable."
Laurinaitis is 10 pounds lighter this season, reporting for training camp at 242 pounds, to better handle pass-defending duties in Fisher's system. In his first three seasons, Laurinaitis needed a bigger body to fend of blocks from linemen.
In the offseason, he worked with a nutritionist that provided calorie counts for foods.
"Now, a lot of it is flowing," Laurinaitis said during camp. "Strength has gone up, just a lot more running and functional training."
Fisher has referred to Laurinaitis as a "captain of the defense."
Information from The Associated Press was used in this report.