The move, first reported by ESPN's Adam Schefter, reunites Freeney with Lions head coach Jim Caldwell, who was the Colts' offensive coordinator and head coach for part of Freeney's tenure in Indianapolis.
The 37-year-old Freeney, in his 16th season, will be joining his sixth NFL team.
Freeney had three sacks in four games with the Seahawks. The seven-time Pro Bowler was signed last month after Seattle lost pass rusher Cliff Avril to a neck injury.
All seven of Freeney's Pro Bowl appearances came in his 11 seasons with the Colts from 2002-2012. He also played for the San Diego Chargers (2013-14), Arizona Cardinals (2015) and Atlanta Falcons (2016) in addition to his short stint in Seattle.