The Lions also placed DE Austin Bryant on the active/PUP list.
Mack, 23, is a former fifth-round pick by the Ravens in the 2019 NFL Draft. He was entering the second year of his four-year, $2.8 million rookie contract when the Ravens opted to waive him on Saturday.
In 2019, Mack appeared in one game but has yet to record any statistics.
During his four-year college career at Texas A&M, Mack recorded 108 total tackles, 27 tackles for loss, eight sacks, two pass defenses, and two forced fumbles.