A spokesman for RMG Connect could not comment on the circumstances of Bradbury's departure, but confirmed he was no longer with the agency.
His decision to leaves comes after Hipperson made a raft of senior appointments at the agency after joining in February this year.
In March, the agency hired Dan Cole, senior copywriter at Saatchi & Saatchi, as a creative partner, along with John Henderson and David Douthwaite. John Reeves was promoted after three years service.
Bradbury joined the agency in January 2005 to head its creative team, having previously worked at Saatchi & Saatchi.
He is credited with orchestrating RMG Connect's winning of the direct recruitment award at the 北京赛车pk10 Awards in 2006, for the agency's work on the domestic violence corporate alliance account for the Home Office.
Details of who will be taking over from Bradbury are not yet known.