Bromley was of a Shropshire gentry family, which traced its origins to Eccleshall in the neighbouring county of Staffordshire and the family had acquired land through marriage in other neighbouring counties. In the mid-15th century, Thomas's grandfather married an heiress from Malpas, Cheshire. Their allies, the Hills, had married apparently into the same family, not disdaining marriage for gain, although the family concerned had declined from the medieval nobility to merely yeoman status. Thomas's uncle William was married to a Hill and the two families were to prosper together in the 16th century.