Callister was born on 16 February 1893, in
Chute, Victoria near
Ballarat, son of Rosetta Anne (née Dixon) and William Hugh Callister, a teacher and postmaster. The second son of seven children, he attended the
Ballarat School of Mines and
Grenville College, and later won a scholarship to the
University of Melbourne. He gained a Bachelor of Science degree in 1914 and a Master of Science degree in 1917. In early 1915, Callister was employed by food manufacturer Lewis & Whitty, but later that year he enlisted in the
Australian Imperial Force. After 53 days, however, he was withdrawn from active service on the order of the
Minister for Defence and assigned to the Munitions Branch, making explosives in Britain due to his knowledge of chemistry. He worked on munitions in England, Wales, and then in Scotland, at
HM Factory Gretna where he worked as a shift chemist. Whilst at Gretna he was elected as an Associate of the
Institute of Chemistry in 1918. Following the end of
World War I, he met and married Scottish girl Katherine Hope Mundell and returned to Australia and resumed employment with Lewis & Whitty in 1919. ==The invention of Vegemite==