William Parry (or Parrie) (died 2 March 1585) was a Welsh courtier and spy. He considered assassinating Elizabeth I of England, and was executed.
He was the son of Harry ap David, a gentleman of Northop, Flintshire, and his wife Margaret, daughter of Pyrs or Peter Conway, archdeacon of St. Asaph and rector of Northop. Harry ap David, on his son's account, was in the guard to Henry VIII, and died about 1566, leaving fourteen children by his first wife and sixteen by his second, Parry's mother. Parry was originally named William ap Harry.
Parry was apprenticed to John Fisher of Chester, who had some legal knowledge in law; he attended a grammar school, and made attempts to escape from his master. He went to London to seek his fortune. A marriage with a Mrs. Powell, widow, and daughter of Sir William Thomas, brought him some income.
In the household of William Herbert, 1st Earl of Pembroke until the Earl's death in 1570, Parry then entered the Queen's service. He appears to have involved himself in financial difficulties, despite a second marriage to money.
Parry sought a commission from Lord Burghley to spy on Catholics on the Continent of Europe, with the idea of escaping his creditors. On a first trip abroad he visited Rome, Siena, and other places. In 1577 he was back in England, though still short of money. In 1579 he left the country again abruptly; he wrote to Burghley from Paris excusing his conduct, and Burghley put Anthony Bacon in touch with him. Around this time Parry covertly joined the Roman Catholic Church.
In 1580 Parry again returned to England. in November, after renewed proceedings by his creditors, he made a personal assault on Hugh Hare, one of them, in the Inner Temple. Parry was convicted and sentenced to death. He received a pardon from the Queen. He found sureties for his debts, one of whom was Sir John Conway, a connection of his mother's.