Sir Thomas de Rokeby was a 15th-century English soldier, Knight of the Shire and High Sheriff of Yorkshire. He was born into a well-known north Yorkshire family with a seat at Mortham on the banks of the Tees. An earlier Thomas de Rokeby who died in 1356 had been Lord Lieutenant of Ireland; he was probably a brother of the younger Thomas' great-grandfather. He later served in the army of Henry V of England in France. He fought at the Battle of Agincourt in 1415, was present throughout most of the siege of Rouen in 1418–1419 and marched through Paris in triumph in 1420.