Thomas, 2nd Earl of Lancaster was an English nobleman of the first House of Lancaster of the royal Plantagenet Dynasty. He was Earl of Lancaster, Leicester, and Derby from 1296 to 1322, and Earl of Lincoln and Salisbury jure uxoris from 1311 to 1322. As one of the most powerful barons of England, Thomas was one of the leaders of the baronial opposition to his first cousin, King Edward II.

Earl of Leicester is a title that has been created seven times. The first title was granted during the 12th century in the Peerage of England. The current title is in the Peerage of the United Kingdom and was created in 1837.