"Back to where it all begin but as a better Player and Man," Sims-Walker wrote in a post on his Twitter feed.
The move brings Sims-Walker back to the team that drafted him in 2007, just seven months after the Jaguars told him they were moving in a different direction. The Jaguars did not re-sign Sims-Walker in March, opting to sign Jason Hill to a two-year deal instead.
"He came in here; he grew up as a man here," Jaguars running back Maurice Jones-Drew said. "Obviously his time in St. Louis wasn't what he wanted it to be, so we'll welcome him back with open arms. Get him back here and help this offense out as much as possible."