Jackson was one of the top wideouts available in free agency once San Diego decided not to give him the franchise tag. It didn't take him long to hook up with Tampa Bay and quarterback Josh Freeman, in whose honor Jackson got all those 5s in the deal; Freeman wears uniform No. 5.
The contract, negotiated by Schwartz and Feinsod Agency, will pay Jackson $13 million in each of his first two years, then $10 million for the third year.
Sources told ESPN NFL Insider Adam Schefter earlier Tuesday that Tampa Bay is also trying to sign free-agent guard Carl Nicks.
Nicks, a two-time Pro Bowler at guard, was voted first-team All-Pro by The Associated Press in 2011, along with the Saints' other starting guard, Jahri Evans. That hasn't happened since 1953, with Detroit's Lou Creekmur and Dick Stanfel.
While Nicks is just cashing in now, Evans signed a seven-year, $56.7 million contract with the Saints in 2010. Nicks was drafted by the Saints in the fifth round of the 2008 draft.
Jackson was a Pro Bowler last season after catching 60 passes for 1,106 yards and nine touchdowns, but his departure from San Diego wasn't exactly a surprise.
The 6-foot-5 Jackson had consecutive 1,000-yard seasons in 2008-09 before getting embroiled in a nasty contract spat that cost him much of the 2010 season.
Jackson's original five-year contract expired after the 2009 season. But because 2010 was an uncapped year, he would have needed six seasons to become an unrestricted free agent.
Unhappy that he didn't get a long-term deal, Jackson refused to sign a $3,268,000, one-year tender as a restricted free agent. He sat out the first seven games and then reported in time to serve a three-game suspension on the roster exempt list -- he was placed there in a hardball move by Chargers general manager A.J. Smith. He was on the active roster for the final six games to accrue a season toward unrestricted free agency.
When Jackson hadn't signed the tender by that June 15, the Chargers slashed their offer to 110 percent of his 2009 salary, or $583,000. Due to the games he missed, he made less than $300,000 in 2010.
In his first game back, Jackson lasted only two plays before limping off the field with a strained right calf. He missed the following game and finished the season with 14 catches for 248 yards and three touchdowns.
Jackson had two DUIs and was cited for driving with a suspended license and expired tags on the morning of the Chargers' playoff loss to the New York Jets in January 2010.
The Chargers placed the franchise tag on Jackson last season, when he earned around $11 million.
Information from The Associated Press contributed to this report.