The deal for Jackson, who played the past three seasons with the Atlanta Falcons, is worth $8 million.
For several years, Jackson has been regarded as one of the best defensive lineman in the league against the run. Because off his size, conservatively listed at 345 pounds, Jackson usually commands double-team blocking. He played in the 370s for Atlanta last year, but a source said he weighed 349 pounds at the Detroit physical.
The 12-year veteran will be joining his fifth different NFL franchise. He entered the league as a sixth-round pick of the Oakland Raiders in the 1997 draft. He played five seasons for the Raiders and then went to the New Orleans Saints (2002-03), Green Bay Packers (2003-05), and the Falcons (2006-08).
Jackson, 36, is a graduate of Knoxville College.
Jackson and the Lions agreed to most of terms of the contract terms on Tuesday, but he had to pass a Wednesday physical exam before the deal could be officially signed.
In 12 years, Jackson has collected 327 tackles, 35 1/2 sacks and 17 pass deflections. In terms of rushing the passer, his best season came with the Raiders in 2000 when he had a career-best eight sacks. Over the past six seasons, however, Jackson has only five sacks and is regarded mostly as a two-down player who doesn't provide much push up the middle.
Jackson is now viewed as a terrific defender against the run, and two years ago, he led the NFL in tackles for losses.
Last December, Jackson was one of eight players in the league found to have used an illegal substance. His status has yet to be resolved, but Jackson could face a four-game suspension by NFL officials.
Len Pasquarelli is a senior writer with ESPN.com.