The 24-year-old had a fine season for the Rams in the 2013 campaign, notching 19 sacks on his way to becoming an All-Pro player.
The club has recognised his form by handing him a new six-year deal worth $65.6m, with $45.2m of the contract guaranteed.
"This is a very happy day for the St. Louis Rams and Robert Quinn," general manager Les Snead told the club's official website.
"Since his arrival, Robert has progressed into one of the top disruptive forces at the defensive end position."
Quinn has recorded 111 tackles and 34.5 sacks in his four years with the Rams.