Henry de Vere, 18th Earl of Oxford KB (24 February 1593 – June 1625) was an English aristocrat, courtier and soldier.
He was born on 24 February 1593 at Newington, Middlesex, the only son of Edward de Vere, 17th Earl of Oxford, by his second wife, Elizabeth Trentham. He succeeded his father as earl on 24 June 1604.
He is said to have been educated at Oxford University. He was admitted a member of the Inner Temple in November 1604, and was created M.A. of Oxford on 30 August 1605. He was made a knight of the Bath on 3 June 1610, and keeper of Havering Park on 15 November 1611. In his youth he had a reputation for debauchery.
On his mother’s death, early in 1613, he inherited a share of her fortune, and set out on an extended foreign tour. From Brussels he made his way through France to Italy. At Venice in 1617 he offered to raise a body of volunteers for the service of the republic, and he exerted himself to obtain the release of his kinsman Sidney Bertie, who had fallen into the hands of the Inquisition at Ancona.
While Oxford was still abroad, he was involved vicariously in a tangled family drama. Against the wishes of Sir Edward Coke, Lady Hatton, Coke's wife, offered Oxford the hand of her daughter Frances Coke, whom the king wished to marry to Sir John Villiers, the brother of George Villiers, 1st Duke of Buckingham. Lady Hatton was in fact obstructing Coke's plan to improve his standing at court, with Buckingham; she did this by claiming Frances was already promised to Oxford, and by placing Frances out of reach in houses of allies. This failed matchmaking laid the seeds of a future quarrel between Buckingham and Oxford, though the Villiers marriage for Frances went ahead in September 1617. Oxford returned to England in October 1618. On 22 May 1619 he was admitted to the hereditary office of Lord Great Chamberlain.