Rotherham United have been searching for a new coach since Wednesday following the sacking of Alan Stubbs , who lasted just four months in the role.
Jackett has been out of work since he left his role as Wolverhampton Wanderers boss before the start of the season after new owners took over the club.
The Championship outfit announced that the 54-year-old has signed a three-year deal and will be in the dugout for tomorrow’s league match against Reading at the New York Stadium.
The Millers have secured victory in just one of their 13 Championship games this season and they have suffered defeat in their last six.
The club are currently at the bottom of the table, six points from safety.