Reiff agreed to a one-year deal worth up to $12.5 million, with $10 million likely to be earned, according to ESPN's Adam Schefter.
Reiff, 33, is the second offensive lineman to join the Bears this week. Chicago signed Michael Schofield on Monday after he was brought in for a workout last weekend.
"The experience and the flexibility those guys have, it's just outstanding," coach Matt Eberflus said. "That enables us to do a lot of different things. We're in a much better spot with those two guys on our roster than we were 24 hours ago."
A first-round pick by Detroit in 2012, Reiff spent most of his first four NFL seasons at left tackle before he switched to right tackle in 2016. Reiff signed with Minnesota in 2017 as a free agent and moved back to left tackle for the next four seasons. In 2021 Reiff was with Cincinnati, where he started 12 games at right tackle.
Schofield boasts similar position flexibility, having spent his seven-year NFL career shifting between right tackle and right guard, starting 13 games at right guard in 2021 for the Los Angeles Chargers.
Both moves come less than a week after Bears guard Dakota Dozier underwent season-ending surgery to repair a torn ACL in his left knee, sources told ESPN's Jeremy Fowler.
The Bears experimented with a handful of combinations along the offensive line during spring practices. Fifth-round rookie Braxton Jones earned ample reps at left tackle with the first-team unit after Chicago moved Teven Jenkins to right tackle with the twos. Larry Borom settled in at right tackle with the ones after receiving several reps at left tackle during early offseason practices.
"We've got a ways to go," Poles said. "If you think about the offseason program, everything's done in helmets, so we've still got pads. I thought they [Jenkins and Borom] both did a pretty good job. I know that they were challenged in the offseason to continue to work on their bodies to adapt to the scheme we're running. We'll see here in a couple of hours how they did this offseason. But again, I think the way to look at it is just added competition for guys to compete and you gotta go. You gotta go. You gotta perform, and that's for everyone."
Eberflus would not name who will be starting at left and right tackle with the first-team offensive line when the Bears take the field for their first training camp practice Wednesday. Reiff's decade-long experience could put him in line to start at left or right tackle, while Schofield's 82 career starts could give him the inside track to filling the void at right guard.
The offensive line remains a question mark for the Bears entering training camp. Chicago allowed an NFL-high 58 sacks last season, and Justin Fields was pressured on 36% of his dropbacks, which was the second-highest rate for any quarterback.
Although Eberflus noted no specific deadline for naming the Bears' starting offensive line, the coach said he hoped "the sooner the better."