The son of William Edward Vellacott (a Fellow of the Institute of Chartered Accountants who lived at Budleigh Salterton, Devon), he was educated at Marlborough College and Peterhouse, Cambridge, where he studied the Historical Tripos.[1] He served as Headmaster of Harrow School from 1934 to 1939 and Master of Peterhouse from 1939 to 1954.
On 20 June 1929 he married Hilda Francesca Lubbock, daughter of Sir Nevile Lubbock (1839–1914) and Constance Ann Herschel (daughter of astronomer John Herschel and granddaughter of astronomer William Herschel).