The two sides were reportedly finalizing the deal on Tuesday, after Boldin finished one final workout. The former 49er worked out for Detroit a month ago, but the team was not ready to sign him then.
He has also played with the Arizona Cardinals and Baltimore Ravens. This past season with San Francisco, Boldin had 69 catches for 789 yards and four touchdowns.The 35-year-old is a three-time Pro Bowler. In 13 seasons since getting drafted by Arizona in the second round of the 2003 draft, he has 1,009 receptions for 13,195 yards and 74 touchdowns.
In the all-time ranks, Boldin sits at No. 17 in yards, 12 in receptions, and tied for No. 33 in touchdowns.
During his three seasons with the Baltimore Ravens, Boldin worked under Lions head coach Jim Caldwell, who worked on the coaching staff. He is expected to compete for a roster spot, as starters Marvin Jones and Golden Tate are the only members of the group of receivers who have a roster spot seemingly nailed down.