Sir John Sully (c.1283 – c.1388), KG, of Ruxford and Iddesleigh in Devonshire, was an English knight. He was one of the many deponents who gave evidence in Scrope v Grosvenor (decided in 1389), one of the earliest heraldic law cases brought in England, at which time he stated his age as 105. In about 1362, he was appointed by King Edward III as the 39th Knight of the Garter.