Austin's arrival adds depth to a Dallas receiving group following last week's release of Dez Bryant.
The 5-foot-8, 179-pound Austin is built like the 5-foot-8, 187-pound Dunbar, who totaled 1,068 yards from scrimmage (422 rushing, 646 receiving) in five seasons with the Cowboys (2012-16).
Austin has experience as a tradition running back going back to his prep career at Dunbar High School in Maryland, where he was a two-time Offensive Player of the Year.
Austin originally entered the league in 2013 out of West Virginia as a first-round pick (8th overall) with the Rams, and he has appeared in 75 career games with 50 starts.
In five professional seasons, Austin totaled 194 catches for 1,689 yards and 12 touchdowns. He has rushed for 1,238 yards and nine touchdowns on 184 carries, averaging 6.7 yards per attempt.
The Cowboys could also use Austin on special teams, where he has amassed 1,324 yards and three touchdowns on 158 punt returns, and 451 yards on 25 kickoff returns on his career.