Hewlett joined Swindon 5 years ago from Bristol City, and has played over 200 times for Swindon, but was left out of the squad to face his old club on Wednesday night.
Swindon's official site says that he will not be offered a new contract, but it's also been reported that he was offered a new deal, but he turned it down, but either way he won't be playing for Swindon next season.
Other players out of contract in the summer include Rhys Evans, David Duke, Grant Smith, Matt Heywood, Sammy Igoe, and Brian Howard.