Mills, 30, is a former fifth-round pick of the Bears back in 2013. He spent two years in Chicago before among their roster cuts at the start of the 2015 season and later claimed off of waivers by the Cowboys.
Mills had a brief stint with the Lions before the Bills signed him to their active roster. Buffalo re-signed him to a two-year, $4 million contract back in 2017.
From there, Mills signed a one-year deal with the Dolphins last year but was released with an injury settlement not long later. Mills had a brief stint with the Cardinals before ending up on injured reserve. He signed to the Cowboys practice squad earlier this season and was called up a few weeks ago.
For his career, Mills has appeared in 90 games, making 84 starts.