The Bears had been in talks with Miller for about a month after learning first-round draft pick Chris Williams would miss at least the first half of the season while recovering from back surgery. The durable Miller, entering his 13th year, has started 160 of his last 162 games -- 46 with the Bears the past three seasons.
He helped Chicago reach the Super Bowl two years ago and played in one with St. Louis. The Bears released him in February to avoid paying a roster bonus.
A fifth-round draft pick by the Rams in 1996, Miller has blocked for a 1,000-yard rusher in seven of his 12 NFL seasons with St. Louis, Tennessee Titans and Chicago.
The Bears released rookie tackle Kirk Barton, a seventh-round draft pick out of Ohio State.