Jackson, who will turn 30 in July, is considered a better fit for offensive coordinator Dirk Koetter's offense because he's a better pass catcher.
Jackson has rushed for 10,135 yards and 56 touchdowns in the NFL since being taken in the first round (24th overall) of the 2004 draft. He also has caught 407 passes for 3,324 yards and eight touchdowns.
Jackson, who has been to three Pro Bowls, was negotiating with the Green Bay Packers and the Falcons.
Jackson has played on some pretty poor teams in St. Louis and wanted to play for a contender.
The Falcons reached the NFC championship game last season before losing 28-24 to the San Francisco 49ers.
Jackson helped the Rams reached the playoffs after his rookie season in 2004. The Rams beat Seattle 27-20 in the wildcard round before getting pummeled by the Falcons 47-17 in the divisional round at the Georgia Dome.
The Falcons were elated to get Jackson over NFC rival Green Bay.
Earlier in the week, Falcons coach Mike Smith spoke about the franchise’s status around the league, which also was a factor in attracting Jackson.
“I really think it speaks volume for where we at as a football team,” Smith said. “Mr. (Arthur) Blank talks about it all the time. I talk about it and it comes from Arthur about being a relevant team. Thomas has done an outstanding job with providing us with players.
“We know that the roster changes every year, but we are a relevant football team in the National Football League. What I mean by relevant is you want to be in the conversation at the end of the season and having an opportunity to play in that second season because that’s what everybody is shooting for.”
By coming to the Falcons, that’s what Jackson is shooting for.