On the death of Malcolm IV his brother, William, became the king of the Scots. William was crowned at Scone.

King Henry II returned from Normandy and spent Easter at Windsor Castle where he was joined by William, King of Scotland and his brother David. The English king knighted David at this event.

The baronial rebellion against King Henry II started in 1173 and finished at the battle of Alnwick 1174. It was started by the king's eldest son, the young Henry who went to France to ask the French king, Louis VII to have his father removed from the throne. In England the barons rose up against King Henry and were assisted by the Scottish king, William I.  ^[1]

King William of Scotland targeted several key fortifications in northern England, particularly in Northumberland and Cumberland in an attempt to seize territory while King Henry II was preoccupied with the broader revolt against his son. Castles that he attempted to capture included Carlisle Castle, Newcastle Castle, Prudhoe Castle and Alnwick Castle. All of these castles managed to be defended against the Scottish King's attacks and sieges.

King William of Scotland allied with Henry II's rebellious sons, particularly Henry the Young King, to weaken Henry's hold on England. William crossed the English border with his forces, leading raids into Northumberland and Cumberland attacking English towns and castles, but was bravely pushed back by supporters of the King of England. In the autumn, after causing widespread disruption, William withdrew to regroup for a renewed offensive in spring 1174.

William I, king of Scotland invaded England to help fight in the baronial rebellion against Henry II. The Scottish King attacked the castle at Prudhoe but was unable to capture it. William was captured at the Battle of Alnwick and the rebellion came to an end. He was transported to Falaise in Normandy where he would later sign a peace treaty.

Captured by the English, William I of Scotland was forced to sign the Treaty of Falaise. The treaty made Scotland a feudal possession of England and William and his nobles swore fealty to Henry II. William had to hand over several castles to the English in return for his freedom. One of these was Stirling Castle. This treaty was overruled by King Richard I in return for funds paid by Scotland that Richard needed for his crusade in 1189. ^[2]

William I of Scotland gave Richard I of England 10,000 marks for the Crusade. This overturned the Treaty of Falaise which William had to sign when captured in 1174. ^[2]

William the Lion of Scotland was eager to support John's claim to the throne of England in exchange for ownership of the northern territories of England iincluding Northumberland and Cumberland. John had promised to honour these demands while back in Normandy as long as the Scottish King kept the peace until he arrived. Through mediation the threat of conflict between England and Scotland was put aside. This allowed John to concentrate his efforts against France where King Philip was causing problems.

During a tour of the Midlands, John received homage from William 'the Lyon', King of Scotland at Lincoln. William was looking to move into the areas of Northumberland, Cumberland, and Westmoreland. John on the other hand ensured that those areas were controlled by Barons he could trust. ^[3]

William, King of the Scots was prepared to give John his eldest son, Alexander as hostage to keep the peace between the two countries. William was also eager that Alexander should become King of the Scots after himself. Earning the trust of John was to be repaid later when John sent an army to Scotland to help William put down a rebellion. ^[3]

William, the King of Scotland died.