Sir Thomas Dagworth (1276 – 20 July 1350) was an English knight and soldier, who led the joint English-Breton armies in Brittany during the Hundred Years' War.

In 1346 he led a small English force in Brittany in support of John de Montfort's claim on the dukedom.

On 9 June, Dagworth's force was attacked by Charles' much larger army at Saint-Pol-de-Léon.

The next year, on 20 June, he claimed an even more famous victory at the Battle of La Roche-Derrien, where he captured Charles of Blois.

He was killed in an ambush on 20 July 1350, near Auray, a few miles west of Vannes, by a Franco-Breton force under Raoul de Caours.