The announcement was official by the Packers' Executive Vice President, General Manager and Director of Football Operations Ted Thompson on Thuursday, according to the team's official site.
Harrell participated in workouts with the Cleveland Browns after being cut by the Canadian Football League's Saskatchewan Roughriders earlier this year.
Harrell spent last season on the roster with Saskatchewan.
"It went well," Harrell told the Green Bay Press Gazette after OTAs on Wednesday. "I thought I did all right. It wasn't the greatest I've ever thrown the ball, but I threw the ball pretty well."
The 6-foot-2 quarterback set numerous records at Texas Tech as a three-year starter with the Red Raiders, leading Tech to its highest Bowl Championship Series ranking in 2008 (No. 2) en route to an 11-2 season. Harrell finished his Red Raider career with 15,793 yards passing and an NCAA FBS record 134 career touchdown passes.
More on Harrell later today.