The 32-year-old Holt agreed to a creative contract that grows financially based on the way he plays. The deal, a source told ESPN.com's John Clayton, calls for three years with base salaries totaling $13 million. While there is no signing bonus, the first year of the contract is guaranteed.
The Jaguars worked a similar deal with left tackle Tra Thomas that rewards him with bigger salaries based on his playing time and his performance.
Holt chose the Jaguars over the Tennessee Titans, among other teams that were interested. He was released by the Rams and was considered one of the top receivers available via free agency.
The deal lessens the need for Jacksonville to get a receiver early in this weekend's NFL draft and gives the franchise its biggest weapon at the position since Jimmy Smith retired in 2006.
The Jaguars still might select a receiver with the No. 8 pick, especially since Holt will be 33 years old this summer and has been slowed by knee problems in recent years. Texas Tech's Michael Crabtree and Missouri's Jeremy Maclin are expected to be top-10 picks.
Jacksonville has been searching for a No. 1 receiver since Smith's retirement. The team selected Reggie Williams (2004) and Matt Jones (2005) in the first round in consecutive years, but parted ways with the troubled receivers this offseason. The Jaguars chose not to re-sign Williams after five disappointing seasons and released Jones after he violated a plea agreement stemming from a drug charge.
Jacksonville also got rid of Jerry Porter in February. The Jags paid Porter $11 million last season, but he finished with 11 catches and got blamed for chemistry issues in the locker room.
Northcutt has never shown he could be a go-to receiver. Walker hasn't been fully healthy during his two years in the league. And Williamson, a former first-round pick, played sparingly last season after getting trading to Jacksonville following three miserable years in Minnesota.
Holt certainly boosts the Jaguars' wideout position. The seven-time Pro Bowler ranks 11th on the NFL's career list with 869 receptions. He caught 64 passes for 796 yards and three touchdowns for St. Louis last season. The Rams released him in March days before he was due a $1.25 million roster bonus.
Information from ESPN.com's John Clayton and The Associated Press was used in this report.