The 34-year-old from Goldthorpe was promoted from under 16s coach to assistant by Daniel Stendel in January and helped the Reds to promotion from League One.
After Stendel was sacked in October, former Barnsley player Tonge worked alongside caretaker Adam Murray but, after last week's arrival of new head coach Gerhard Struber and two other coaches, he has left Oakwell.
A club statement read: "Dale Tonge has left his role as First Team Coach. Dale’s contribution to the success of the 2018/19 promotion winning campaign will live long in the club’s memory, adding further memories to his playing career at Oakwell, where he also achieved promotion. Tonge stepped into the role as First Team Coach at a vital time during last season. Everyone connected to Barnsley Football Club would like to thank him for his efforts in securing a memorable promotion."
Murray will remain at the club as one of Struber's first team coaches.