Kupp's deal comes two days after teammate Jalen Ramsey signed a five-year, $105 million extension that included $71.2 million guaranteed at signing -- the most lucrative contract for a defensive back in NFL history.
In the immediate aftermath of Ramsey's extension, coach Sean McVay expressed optimism that the Rams would also complete a deal with Kupp before the season opener Sunday against the Dallas Cowboys.
So did Kupp, who turned 27 in June.
"I'd love to be a Ram long term," Kupp said earlier this week. "I love it here. I love my teammates, I love the coaches."
Ramsey took to Twitter to celebrate news of Kupp's deal.
Kupp and receiver Robert Woods are expected to be among Goff's top targets in 2020. Josh Reynolds and rookie Van Jefferson replace Brandin Cooks, whom the Rams traded to the Houston Texans over the offseason.
A third-round pick from Eastern Washington in 2017, Kupp was scheduled to earn $2.1 million in the final season of his rookie deal.
After tearing the ACL in his left knee midway through the 2018 season, Kupp returned last season with a vengeance. He caught 94 passes for 1,161 yards and 10 touchdowns, all career bests. In a Week 8 victory over the Cincinnati Bengals in London, he caught seven passes for 220 yards and a touchdown.
Kupp's 10 touchdown receptions ranked second in the NFL behind Detroit Lions receiver Kenny Golladay, who had 11, and he ranked fourth among all receivers with 544 receiving yards after the catch, according to ESPN Stats & Information.
The fourth-year pro also has excelled in the red zone since his rookie season. Kupp ranks in the top 10 in red zone receptions (33), receiving yards (233) and receiving touchdowns (15).
In 39 career games, including 28 starts, Kupp has caught 196 passes for 2,596 yards and 21 touchdowns.