Born in the western New South Wales bush town of Cobar on 8 December 1914, Toshack was one of five children of a stationmaster. Orphaned at the age of six, he was raised by relatives in Lyndhurst in the central east of the state, and played his early cricket and rugby league for Cowra. At this time, Toshack's ambition was to play rugby league for Australia. One of his childhood friends, Edgar Newham, also played both sports and wanted to play Test cricket. However, the town's doctor, a local community leader, advised that they were targeting the wrong sport, and the two boys followed his recommendation. Newham later played rugby league for Australia.