 Minnitt was born in Southgate in London in 1894, the youngest of five sons of Mary Ann Smith (1854-1943) and William Robinson Minnitt (1858-1927).Educated at the Hugh Myddleton School in Islington, aged 14 he was the London Junior Boxing Champion; later, he followed his father into working for the General Post Office (GPO) before serving with the Coldstream Guards during World War I.He was sent to France where he suffered injuries from mustard gas which affected him for the rest of his life.