The Falcons announced the signing on Thursday.
Marlowe, 29, began his career by playing three seasons with Carolina before two seasons with Buffalo.
Marlowe may compete with second-year player Richie Grant, a second-round draft pick in 2021, for a starting job.
Marlowe had two interceptions with Buffalo in 2020. He had a fumble recovery and two passes defensed with the Lions last season.
The Falcons have made their secondary a focus in free agency. They also signed former Raiders cornerback Casey Hayward and former Chicago cornerback Teez Tabor.