Hardy has spent the last two days in Texas and finally agreed terms on Wednesday on a one-year deal that could pay him $13m if he meets a series of incentives.
The deal has been agreed despite Hardy being under a suspension cloud.
Hardy was placed on the inactive list before the second game of the 2014 season and the commissioner’s exempt list before the third game until his domestic violence case was resolved.
Although the charges were dropped, Hardy remains on the exempt list as the NFL conducts its own investigation into whether he violated the league’s personal conduct code.
The former Carolina Panthers end could also face a suspension for part of the 2015 season, with reports hinting it could be between four and six games.
The 26-year-old was a Pro Bowl pick in 2013 after leading the franchise with 15 sacks, and he fills a big hole in the Dallas roster, as the Cowboys managed only 28 sacks as a team last season, Jeremy Mincey leading them with six.