 McCreery was educated at Bilton Grange, St Michael's Preparatory School, Westgate-on-Sea and Eton College.Six months after the outbreak of the First World War in August 1914, McCreery sat the entrance examination for the Royal Military College, Sandhurst, only days after his seventeenth birthday, the minimum age, and finished 12th of 212 entrants.On 11 August 1915, McCreery was commissioned as a second lieutenant into the 12th (The Prince of Wales's Royal) Lancers, but instead of joining his regiment in France, was posted to the 6th Reserve Regiment of Cavalry based in Dublin for further training in cavalry tactics.