Heathcoat-Amory was elected a Devon County Councillor in 1932 and worked in textile manufacturing and banking. He was commissioned a second lieutenant in the 11th (Devonshire) Brigade of the Royal Artillery (Territorial Army) on 31 July 1920, promoted to lieutenant in the 96th (Royal Devonshire Yeomanry) Field Brigade on 31 July 1922 and promoted to captain on 1 September 1926. He was promoted to major on 1 October 1935. During the Second World War, he was wounded and captured during Operation Market-Garden. He retired on 1 September 1948 with the honorary rank of Lieutenant-Colonel.