The deal is worth $80 million, a source told ESPN's Adam Schefter.
"Brandin Cooks has shown himself to be a class act on and off the field since the first day he joined our team," HC Sean McVay said in a statement. "He's a proven professional in this league and signing him to a long-term contract was always our goal."
Acquired in an offseason trade with the New England Patriots, Cooks, 24, has yet to play a snap for the Rams, but coach Sean McVay liked what he saw from the receiver throughout the offseason program. Cooks said he knew he wanted to sign a long-term contract shortly after arriving at the team's training facility and observing the culture established by McVay, the story said.