The deal is worth approximately $2.36 million and includes a signing bonus of $750,000.
The agreement with Calhoun caps a flurry of activity on a day in which Detroit wrapped up three other draft picks. The team also came to terms with late round picks Jonathan Scott (fifth round), Dee McCann (sixth round) and Anthony Cannon (seventh round).
Fred Matua, another seventh round pick, was signed Tuesday night.
With Calhoun in the fold, the Lions are left with only first-round pick Ernie Sims and second-rounder Daniel Bullocks unsigned. The team must move swiftly to complete deals before tomorrow evening's training camp deadline.
All players are required to report to the team's Allen Park facilities by late Thursday.
Calhoun, a Wisconsin product and the 10th player picked in the third-round, is considered the complete package and many analysts pegged him as a steal in the April draft. In his final season at UW, Calhoun carried the ball 348 times for 1,636 yards in addition to a school-record 22 touchdowns. He also tallied 53 receptions for 571 yards.
With a scat back mentality (he stands just 5'9, 202 lbs), Calhoun will see time on the field as a third down runner, but perhaps not as frequently as veteran Shawn Bryson. Still, he possesses track speed, a seamless pass-catching ability, and shiftiness in the open field.
Depending on the status of incumbent Eddie Drummond, Calhoun could also be valuable as a return man, seeing time at both punt and kick returner.