Warkworth Castle is a ruined medieval castle in Warkworth in the English county of Northumberland. The village and castle occupy a loop of the River Coquet, less than a mile from England's north-east coast. When the castle was founded is uncertain: traditionally its construction has been ascribed to Prince Henry of Scotland, Earl of Northumbria, in the mid-12th century, but it may have been built by King Henry II of England when he took control of England's northern counties. Warkworth Castle was first documented in a charter of 1157–1164 when Henry II granted it to Roger fitz Richard. The timber castle was considered "feeble", and was left undefended when the Scots invaded in 1173.

Roger's son Robert inherited and improved the castle. Robert was a favourite of King John, and hosted him at Warkworth Castle in 1213. The castle remained in the family line, with periods of guardianship when heirs were too young to control their estates. King Edward I stayed overnight in 1292 and John de Clavering, descendant of Roger fitz Richard, made the Crown his inheritor. With the outbreak of the Anglo-Scottish Wars, Edward II invested in castles, including Warkworth, where he funded the strengthening of the garrison in 1319. Twice in 1327 the Scots besieged the castle without success.

John de Clavering died in 1332 and his widow in 1345, at which point The 2nd Baron Percy of Alnwick took control of Warkworth Castle, having been promised Clavering's property by Edward III. Henry Percy, 1st Earl of Northumberland, added the imposing keep overlooking the village of Warkworth in the late 14th century. The fourth earl remodelled the buildings in the bailey and began the construction of a collegiate church within the castle, but work on the latter was abandoned after his death. Although The 10th Earl of Northumberland supported Parliament during the English Civil War, the castle was damaged during the conflict. The last Percy earl died in 1670. In the mid-18th century the castle found its way into the hands of Hugh Smithson, who married the indirect Percy heiress. He adopted the surname "Percy" and founded the dynasty of the Dukes of Northumberland, through whom possession of the castle descended.

In the late 19th century, the dukes refurbished Warkworth Castle and Anthony Salvin was commissioned to restore the keep. The 8th Duke of Northumberland gave custody of the castle to the Office of Works in 1922. Since 1984 English Heritage has cared for the site, which is a Grade I listed building and a Scheduled Ancient Monument.

Although the settlement of Warkworth in Northumberland dates back to at least the 8th century, the first castle was not built until after the Norman Conquest. The town and its castle occupied a loop of the River Coquet. The castle was built at the south end of the town, guarding the narrow neck of the loop. A fortified bridge also defended the approach to the town. The surrounding lowland countryside was favourable for agriculture. When the castle was founded and by whom is uncertain, though traditionally Prince Henry of Scotland, Earl of Northumberland, has been thought responsible. With civil war in South West England, King Stephen of England needed to ensure northern England was secure. To this end, the Treaty of Durham in 1139 between Scotland and England ensured peace. Under the treaty Henry of Scotland became Earl of Northumbria in exchange for ceding control of the castles at Bamburgh and Newcastle to the English. Without them Henry would have needed a new seat from which to exercise his authority, and a new castle at Warkworth may have met the requirement. However, charters show that Henry still controlled Bamburgh Castle after the treaty, and as Warkworth was a modest castle by contemporary standards it may have been founded by someone else. Henry died in 1152 and his son, Malcolm (crowned King of Scotland in 1153), inherited his lands. In 1157 Malcolm travelled to Peveril Castle in Derbyshire, where he paid homage to the new King of England, Henry II. Malcolm surrendered England's northern counties to Henry, including the castles of Bamburgh, Carlisle, and Newcastle, and probably Appleby, Brough, Wark, and Warkworth, though it is possible that Henry II founded Warkworth Castle in 1157 to secure his lands in Northumberland; other contemporary castles in the area were built for this purpose, for instance the one at Harbottle.

The first mention of Warkworth Castle occurs in a charter of 1157–1164 from Henry II granting the castle and surrounding manor to Roger fitz Richard, a member of a noble Norman family. It has been suggested that this charter may have used the term castle to describe a high-status residence on the site, possibly dating from the Anglo-Saxon period, meaning Roger may have built the castle. He owned lands across a wide area, and Warkworth may have been of little significance in the context of his other holdings. When the Scots invaded Northumberland in 1173, although Roger fitz Richard was in the county Warkworth Castle was not defended by its garrison. Its defences at the time were described as "feeble". In 1174 Duncan II, Earl of Fife, raided Warkworth. The contemporary record does not mention the castle, and instead notes that Warkworth's inhabitants sought refuge in the church. When Roger fitz Richard died in 1178 his son and heir, Robert fitz Roger, was still a child. A guardian looked after the family estates until Robert came of age in 1191. He paid the Crown 300 marks in 1199 for confirmation of his ownership of Warkworth, including the castle. Substantial building work at Warkworth Castle is attributed to Robert. A favourite of King John, Robert hosted him at Warkworth Castle in 1213.

Warkworth Castle continued to descend through the family line when Robert fitz Roger was succeeded by his son John in 1214, who was succeeded by his son Roger in 1240. Roger died in 1249 when his son Robert was one year old, and a guardian was appointed to care for the family's estates: William de Valence, half-brother of King Henry III. The castle, characterised by this time by the chronicler Matthew Paris as "noble", remained under the guardianship of Valence until 1268, when it reverted to Robert fitz John. King Edward I of England stayed at Warkworth Castle for a night in 1292. The English king was asked to mediate in a dispute over the Scottish throne and laid his own claim, leading to the Anglo-Scottish Wars. After the Scottish victory at the Battle of Stirling Bridge in 1297, Robert and his son, John de Clavering, were captured. They were subsequently released and in 1310 John assumed control of the family estates. A year later, John made arrangements so that on his death the king would receive all of his property. Between roughly 1310 and 1330 the English struggled to deal with Scottish raids in northern England. Such was the importance of large castles during the Scottish Wars that the Crown subsidised their maintenance and even construction. In 1319, King Edward II paid for a garrison for the castle of four men-at-arms and eight hobilars to enhance the existing force of twelve men-at-arms. Ralph Neville was the keeper of Warkworth Castle in 1322. As he was married to John's daughter, Euphemia, Ralph may have hoped to inherit the Clavering estates, but that did not happen. Twice in 1327 Scottish forces besieged the castle without success.

Around this time, the Percy family was becoming Northumberland's most powerful dynasty. Henry de Percy, 2nd Baron Percy, was in the service of Edward III and was paid 500 marks a year in perpetuity in return for leading a company of men-at-arms. In exchange for the annual fee, in 1328 Percy was promised the rights to the Clavering estates. Parliament declared such contracts illegal in 1331, but after initially relinquishing his claim Percy was granted special permission to inherit. John de Clavering died in 1332 and his widow in 1345, at which point the family's estates became the property of the Percys. While the Percys owned Alnwick Castle, which was considered more prestigious, Warkworth was the family's preferred home. Under the Percys a park was created nearby for hunting, and within the castle two residential blocks were created, described by historian John Goodall as "of unparalleled quality and sophistication in Northumberland". The second baron died at Warkworth in 1352.