[2] Born in 1912 at St Albans, Hertfordshire, the second son of James Grimston, 4th Earl of Verulam and his wife Lady Violet Constance Maitland Brabazon, youngest daughter of Reginald Brabazon, 12th Earl of Meath, he was educated at Oundle School and Christ Church, Oxford.
[3] Grimston was a tobacco farmer in Southern Rhodesia for two years before becoming director and general manager of Enfield Rolling Mills in 1938.
[3] Grimston joined the Royal Air Force Reserve of Officers in 1930 as a pilot being injured in an aircraft accident in 1933.
[3] In 1937 he was commissioned as a Flight Lieutenant in the Royal Auxiliary Air Force and served in Coastal Command during the Second World War.
He married in 1938 Marjorie Ray Duncan (died 1994), daughter of Walter Atholl Duncan (son of Pre-Raphaelite painter Walter Duncan) and wife Clara Ray Parks, maternal aunt of Iona Campbell, Duchess of Argyll and sister-in-law of David Lockhart-Mure Renton, Baron Renton.The Earl and Countess of Verulam had five children:[7] Lord Verulam died in 1973, at the age of 60, and was succeeded in the earldom and other family titles by his only son John as 7th Earl of Verulam.