The 41-year-old Gulutzan had the Stars in playoff contention both seasons, but Dallas faltered down the stretch each time. The Stars were 64-57-9 under Gulutzan, including 22-22-4 in the lockout-shortened 2013 season.
Assistant coach Paul Jerrard also was fired. The team planned an afternoon news conference.
"They are both quality coaches and men, but we have decided to go in a different direction with our coaching staff and we wish them well in their next endeavors," Nill said in a statement.
Assistant coach Curt Fraser and goaltending coach Mike Valley will stay with the club.
Nieuwendyk tried to get Dallas back to the playoffs by adding veterans Jaromir Jagr, Derek Roy and Ray Whitney, but ended up trading Jagr, Roy and longtime captain Brenden Morrow with the team languishing at the trading deadline.