The 37-year-old Freeney became available after the Seattle Seahawks waived him Tuesday following a four-game stint with the club during which he had three tackles and three sacks.
The Lions will be the sixth team Freeney has played for in his career -- and this will mark the first time he has been on two teams in one season.
The move also reunites Freeney with Lions coach Jim Caldwell, who coached him in Indianapolis from 2009 to 2011. Freeney was a Pro Bowler in every season he played under Caldwell, and a first-team All-Pro in 2009.
Completely confused to be in this situation but excited for the future.— Dwight Freeney (@dwightfreeney) November 22, 2017
Lions team president Rod Wood said on WJR radio that Freeney will play as soon as he is ready. Freeney was listed as inactive for the Lions' 30-23 loss to the Vikings on Thursday.
Seattle signed Freeney last month, adding him to a defensive line rotation that had lost Cliff Avril to injured reserve. Freeney recorded a sack in his Seahawks debut, then two more the following week. He averaged 28 snaps over his first three games, then played 17 in Seattle's 34-31 loss to the Atlanta Falcons on Monday night.
Speaking Wednesday, Seahawks coach Pete Carroll called the decision difficult.
"We had to make roster stuff happen," Carroll said. "We've got some injuries and some things we had to deal with. It is a spot where we have some guys that have played that spot. We're a little bit deeper there. We hated to do it, but we had to do something and that's what happened."
Freeney has 341 career tackles, 47 forced fumbles, four fumble recoveries and 125.5 sacks (17th on the all-time list) since being drafted in the first round out of Syracuse in 2002. He has been to the Pro Bowl seven times and was named first-team All-Pro three times.
Freeney was part of the NFL's All-Decade team in the 2000s, and while his snaps have decreased the past three seasons as he has gotten older, he still has 14 sacks since the start of the 2015 season. Among Lions defensive linemen, only Ezekiel Ansah has more (20.5).
The Lions waived wide receiver Jace Billingsley to make room for Freeney on the roster and also signed defensive tackle Christian Ringo from the practice squad.
ESPN's Brady Henderson contributed to this report.