William Thomas (died 18 May 1554), a Welshman from Llanigon, Brecknockshire, was a scholar of Italian and Italian history and a clerk of the Privy Council under Edward VI. Thomas was executed for treason after the collapse of Wyatt's Rebellion under Mary I.
Thomas was a native of Llanigon, and brother to Sir Miles Thomas, clerk of Meline, Pembrokeshire and of Llanigon as shown in the Heraldic Visitations of Wales by Lewis Dwnn. His biographer in The History of Parliament has estimated his birth year as "by 1524". He was presumably educated at Oxford University, where a person of both his name was admitted bachelor of the canon law on 2 December 1529. He may also have been the William Thomas who, along with two other commissioners, inquired into and reported on 27 January 1534 to Thomas Cromwell from Ludlow on certain extortions in Radnorshire and the Welsh marches.
In 1544 he was, according to his own account "constrained by misfortune to abandon the place of his nativity", perhaps for his religious opinions. He spent the next five years abroad, chiefly in Italy, and is mentioned in 1545 as being commissioned to pay some money to Sir Anthony Browne in Venice. In February 1547, when the news of the death of Henry VIII reached Italy, Thomas was at Bologna, where, in the course of a discussion with some Italian gentlemen, he defended the personal character and public policy of the deceased king. He subsequently drew up a narrative of the discussion, and an Italian version was issued abroad in 1552. There is a copy in the British Library bearing the title, II Pellegrino Inglese ne'l quale si defende l' innocente & la sincera vita de'l pio & religioso re d' Inghilterra Henrico ottauo. He also wrote, but did not publish, an English version, to which he added a dedication to the Italian poet Pietro Aretino, and a copy of this, possibly in Thomas's own writing, is preserved among the Cottonian MSS. at the British Museum. Thomas's work is specially valuable as representing the popular view of the character of Henry VIII current in England at the time of his death. It is not free from mistakes, but the Victorian historian James Anthony Froude wrote of it that it had "the accuracies and the inaccuracies" which might be naturally expected "in any account of a series of intricate events given by memory without the assistance of documents".