Boulton was born in 1912 at Braxted Park in Essex to the politician Sir William Boulton, 1st Baronet, and attended Eton College before joining Trinity College, Cambridge. His academic record was not distinguished, but he was able to enter the Inner Temple in 1936 as a practising barrister. At the outbreak of the Second World War, Boulton, who was already with the Essex Yeomanry, joined the Royal Horse Artillery and served in North Africa. In 1940 he took part in Operation Compass, fighting at the Battle of Bardia and then the Siege of Tobruk, where he contracted jaundice and was evacuated to Alexandria. He returned to frontline service soon afterwards but was badly wounded in a land mine explosion.