Sir Thomas de Clifford, 6th Baron de Clifford, also 6th Lord of Skipton (c. 1363 – 1391) was a Knight of The Chamber, hereditary Sheriff of Westmorland, Governor of Carlisle Castle, and Warden of the West Marches.
He was the son of Roger de Clifford, 5th Baron de Clifford and inherited his estates and titles on his father's death in 1389.
In 1384 he was granted the custody of Carlisle Castle for life jointly with with John Neville, and in 1386 was appointed a warden of the west march. In September 1388 he was master of the king's horses. He was summoned to Parliament by Writ from December 6, 1389. He was hereditary High Sheriff of Westmorland from 1389 until his own death in 1391.
In 1391 Clifford was in the Baltic, and became involved in a brawl with Sir William Douglas, an illegitimate son of the earl of Douglas, in which Douglas was killed. Clifford, overcome by remorse, set off for Jerusalem and died in 1391 on an unidentified Mediterranean island.
He married before 1379 Elizabeth (died March 1424), daughter of Thomas de Ros of Helmesley, by Beatrice, daughter of Sir Ralph de Stafford, 1st Earl of Stafford, KG, by whom he had issue. He was succeeded by his eldest son John Clifford, 7th Baron de Clifford.
Lord Clifford is often styled in documents "King's kinsman".