Henry Plantagenet, 3rd Earl of Lancaster (1281 – March 25, 1345) was an English nobleman, one of the principals behind the deposition of Edward II.

He was the younger son of Blanche of Artois and Edmund Crouchback, 1st Earl of Lancaster, Earl of Leicester, who was a son of Henry III of England and Eleanor of Provence.

Henry's elder brother Thomas, 2nd Earl of Lancaster succeeded their father in 1296, but Henry was summoned to Parliament on February 6, 1298/99 by writ directed Henrico de Lancastre nepoti Regis, by which he is held to have become Lord Lancaster. He took part in the siege of Carlaverock in July 1300.

Thomas was convicted of treason, executed and his lands and titles forfeited in 1322. But Henry, who had not participated in his brother's rebellion, petitioned for his brother's lands and titles, and on March 29, 1324 he was invested as Earl of Leicester, and a few years later the earldom of Lancaster was also restored to him.

On the Queen’s return to England with Roger Mortimer, 1st Earl of March in September 1326, Henry joined her party against Edward II, which led to a general desertion of the king’s cause and overturned the power of Hugh le Despenser, 1st Earl of Winchester and his namesake son Hugh the younger Despenser. He was sent in pursuit and captured the king at Neath. He was appointed to take charge of the King, and was responsible for his custody at Kenilworth Castle.

After Edward II's death Henry was appointed guardian of the new king Edward III of England, and was also appointed captain-general of all the King's forces in the Scottish marches.
In about the year 1330, he became blind.

He was succeeded as Earl of Lancaster and Leicester by his eldest son, Henry of Grosmont, who subsequently became Duke of Lancaster.

He married once, to Maud Chaworth, before 2 March 1296/1297. (Some references claim he married Alix de Joinville, but she in fact married Henry's brother John.) With Maud he had seven children:
• Henry of Grosmont, 1st Duke of Lancaster, (about 1300-1360/61)
• Blanche of Lancaster, (about 1305 - 1380)
• Maud of Lancaster, (about 1310-1377)
• Joan of Lancaster, (about 1312-1345)
• Isabel of Lancaster, Abbess of Ambresbury, (about 1317-after 1347)
• Eleanor of Lancaster, (about 1318-1371/72)
• Mary of Lancaster, (about 1320-1362), who married Henry, 3rd Baron Percy and was the mother of Henry Percy, 1st Earl of Northumberland.

He was born in Grosmont Castle, Monmouthshire and died of the plague in Leicester, England. He is interred at The Collegiate Church of St. Mary, Newark, Leicester.