Born at Levuka, Fiji, to medical officer Leighton Kesteven and Caroline Elizabeth, née Eames, he and his family moved to Brisbane in the 1880s and to Sydney in 1891, where Hereward attended Sydney Church of England Grammar School until his father's bankruptcy forced him to leave.
He became technical assistant to the Australian Museum's curator in 1903 and on 18 October 1905 married professional musician Irene "Ivy" Valentine Smith.
In 1934 he ran for the federal election, contesting Earle Page's seat of Cowper for the Douglas Credit Party.
In 1936 he returned to Sydney and became medical director for Goodyear; during the war he worked in armament factories in Lithgow.
His first wife, who had a cerebral haemorrhage in 1936, died after a long illness in 1943 and Kesteven remarried nurse Louise Ray Smith on 24 June 1944 at Darling Point.