The Lions waived Roberts last week after a trade with the New England Patriots was rescinded because of a failed physical.
Roberts, a fourth-round pick by the Lions in the 2017 NFL Draft, was originally sent to the Patriots on Thursday for a future late-round draft selection.
Roberts, listed at 6-foot-5 and 265 pounds, played in 23 regular-season games, including five starts, over the last two seasons. He recorded 13 catches for 146 yards and three touchdowns.
Roberts had nine receptions on 20 targets for 100 yards and three scores last season. He suffered a shoulder injury and was placed on injured reserve to end his 2018 campaign.
The Packers had six tight ends on their current roster before adding Roberts. Veterans Jimmy Graham and Marcedes Lewis, along with 2019 third-round draft pick Jace Sternberger, sit atop the depth chart.