Skarz made 77 appearances for the Millers and 20 this season although he's not pulled the shirt on since November.
Speaking to the clubs official website, boss Steve Evans said; "Joe is a young man who can be described as a fantastic professional and a lad who has given us some fantastic service in his time with the Millers, Over the last few weeks he has become increasingly frustrated at not starting first-team matches and made it clear he needed to play and start on a regular basis."
"The lad leaves the dressing room with all our best wishes and, from a personal level, I can only wish Joe and his family every success for the future. He will always be welcome not only at the AESSEAL New York Stadium, but also at our training ground where his coffee-making skills need some work!" he added.