Believed to have been constructed on the foundations of a Roman fortification, the first castle to be built on the site is attributed to Gamel de Mulcastre, c1258. This structure was enlarged in the 14th century by the addition of a 'Pele' Tower, a fortified watch tower unique to in the Anglo-Scottish border region.

After the battle of Hexham on 15 May 1464, Sir John Pennington gave refuge to King Henry VI at Muncaster Castle. Henry, who had been deposed by Edward IV, still had many loyal followers in the north west of England and Scotland. Despite this, he was eventually captured in 1465 and imprisoned in the Tower of London.

Legend states that, on leaving Muncaster Castle, King Henry left his glass drinking bowl in gratitude, with a claim that the Pennington family would live and thrive at Muncaster so long as it remained unbroken. Today, the bowl - often referred to as the 'luck of Muncaster' - remains wholly intact, and is often displayed in the Great Hall. In 1783 John, Lord Muncaster, commissioned 'Chapels Tower', commemorating the place where the fugitive king was supposedly found by shepherds.

Although extended and altered on several occasions during the 16th and 17th centuries, by the time Sir Joseph Pennington inherited the estate in the 1770s Muncaster Castle was in a serious state of dilapidation. Major alterations and consolidation of the building was undertaken by his son John, 1st Baron of Muncaster, when he moved there with his new bride in 1778. As well as a complete refurbishment, the most significant addition was the Octagonal Library. There was also much planting to the park. In total, Sir John is believed to have spent in the region of £6,000 on the estate, and it is largely through his efforts that Muncaster Castle survived.

In 1862 Gamel Augustus, the 4th Baron Muncaster, commissioned Anthony Salvin to further enhance the castle. He completed the Library in its present form, and created the impressive barrel-vaulted Drawing Room with its fine ceiling created by two Italian Plasterers. Salvin was also attributed to having built the North West tower, intended to compliment the South West Pele Tower. However, recent research suggests that it was built some years earlier in the 1830s. When the 5th and last Lord Muncaster died in 1917, the estate passed to his mother's family the Ramsdens.

Not only is the house of great interest, but some 70 acres of woodland gardens offer a very pleasurable experience to visitors. Largely the work of Sir John Ramsden, Muncaster Castle's gardens are famous for their nationally important collection of rhododendrons, camellias and azaleas, which provide a riot of colour during the spring and summer months. The Terrace Walk, described by John Ruskin as 'The Gateway to Paradise', offers spectacular views across the Eskdale Valley and the Lakeland fells beyond.

Muncaster Castle is also home to the World Owl Trust.