Bush, then playing for the San Francisco 49ers, ran out of bounds on a punt return in a game at the Edward Jones Dome on Nov. 1, 2015, and slipped on some concrete. He suffered a torn lateral meniscus, which ended his season.
"I'm very happy with the verdict," Bush told the Post-Dispatch. "The people spoke and decided very fairly."
Attorneys for the Rams said they plan to file a motion for a new trial. The team declined comment on the verdict.
Bush filed suit in 2016, alleging that the Rams and the public stadium authorities allowed a "a dangerous condition to exist at the Dome." Bush's suit called the area where he fell "a concrete ring of death."
The St. Louis jury ordered the Rams to pay Bush $4.95 million in compensatory damages and $7.5 million in punitive damages.
Bush's original suit was against the St. Louis Rams, St. Louis Regional Convention and Sports Complex Authority and the St. Louis Convention and Visitors Commission. But on Friday, Associate Circuit Judge Calea Stovall-Reid dismissed the convention authority and sports complex, leaving the Rams as the sole defendant.
The Rams moved out of St. Louis to Los Angeles in 2016.
Bush signed a one-year deal with the Buffalo Bills in 2016 but finished with 12 carries for minus-3 yards, seven catches for 90 yards and one touchdown. That was the last year of his 11-year NFL career. He argued that he would have signed a bigger contract if not for the injury.
Bush, 33, is now working as an analyst for the NFL Network.
The Associated Press contributed to this report.