The incident occurred on a site on Kingshill Lane where David Wilson Homes is developing new housing.
The 29-year-old man died at the scene from his head injuries.
Gloucestershire Police said: "Officers are liaising with the Health & Safety Executive in relation to the incident."
A spokesman for David Wilson parent company Barratt Developments said: “On Tuesday afternoon a subcontractor working for Tonic Construction at our David Wilson Homes Pembroke Park site in Cirencester was fatally injured whilst the dumper he was operating overturned.
"We are working closely with the HSE and emergency services regarding this incident, and an internal investigation is underway to establish in more detail what occurred.
"Our thoughts and deepest condolences go out to all of the family, friends and co-workers of the operative involved in this tragic incident. All work at Pembroke Park has currently been stopped."