Cooper, a former 2013 first-round pick with the Arizona Cardinals, was with the New England Patriots and Cleveland Browns last season before joining the Cowboys in December for depth purposes.
He immediately gives the Cowboys a veteran guard to play behind left guard La'el Collins to somewhat help with the loss of Ronald Leary to the Denver Broncos in free agency.
He could also find himself vying for a starting spot at guard if the Cowboys are forced to move Collins to right tackle to make up for the retirement of long-time veteran Doug Free.
The Cowboys hope former third-round pick Chaz Green can develop into a replacement for Free. But he has been injured for much of the past two years and is no sure thing.
The Cowboys have already said that Collins is an option at tackle if needed. He played tackle in college at LSU before the Cowboys decided guard was his best position in the NFL.
Cooper is the latest player to join the Cowboys as insurance and fill holes since the start of the free agency, including the re-signings of receivers Terrance Williams and Brice Butler and the signings of nose tackle Stephen Paea, cornerback Nolan Carroll and defensive end DeMontre Moore.
The Cowboys have lost safeties J.J. Wilcox (Tampa Bay) and Barry Church (Jacksonville), Leary and nose tackle Terrell McClain (Washington). Cornerback Morris Claiborne is close to signing a deal with the Baltimore Ravens.