William le Petit, Petyt, or Lepetit (died after 1360) was an Irish judge who was very briefly Lord Chief Justice of Ireland.
[1] He is referred to as the Irish King's Serjeant in 1338 and as Attorney General for Ireland in 1343, although the two offices are easily confused in this era, due to the lack of precision about their respective roles.
[2] In 1343, and again in 1344, he and his fellow Serjeant-at-law Hugh Brown (who was in office from 1331 to about 1346)[3] received substantial fees for their "good and laudable services" in going with the Lord Deputy of Ireland to several Irish counties to "promulgate and expedite several affairs nearly concerning the King",[4] in addition to the expenses they had incurred.
[5] Accordingly William, whose legal ability and loyalty were vouched for by his colleagues (including, it seems, John de Rednesse), was to have full authority to act as a judge in all the Royal Courts.
[5] He had two powerful patrons in James Butler, 2nd Earl of Ormond, and his wife Elizabeth Darcy, who employed le Petit as her attorney.