The Gruffydd (Griffiths) family, descended from Ednyfed Fychan—the 13th-century steward to Llywelyn the Great—rose to prominence as part of the Welsh uchelwyr, the gentry class that assumed regional leadership after the fall of the Princes of Gwynedd in 1282. They became one of the most influential families in northwest Wales, gradually owning estates across Anglesey and Caernarfonshire between the 1300s and 1600s.

After losing his lands for supporting the Glyndŵr Rising, Gwilym ap Gruffydd was pardoned and was allowed to reclaim his property and also to buy the estates of other dispossessed rebels. His later marriage to Joan Stanley helped secure English political privileges for his family and he built a fortified manor house on the site. A generation later, the Penrhyn estate became the subject of a dramatic inheritance dispute when Gwilym’s grandson Edward Griffith died in 1531, leaving only daughters and a tangle of marriages whose legitimacy was contested.

Edward had married two sisters in succession, Jane, who died shortly after marriage, and Agnes. His father disapproved of Agnes and was delighted when Edward married Jane Puleston, probably because of her financial connections. He had three daughters with Jane Puleston who after Edward’s death, claimed that they were entitled to his estate. However, his brother Rhys argued that the marriage to his first wife, Agnes was the only legal ceremony and as they had had no children [there was a rumour that the marriage had not been consummated] Rhys was the sole heir to the estate.

At the time, Edward Griffith’s marital troubles were compared to Henry VIII’s, as the king was seeking to annul his marriage to Catherine of Aragon, who had previously been wed to his brother Arthur. Drawing on the royal precedent, Edward questioned whether his own marriage to Agnes was invalid because he had earlier married her sister Jane, or whether his later marriage to Jane Puleston was bigamous because he remained legally bound to Agnes. As a result, the legitimacy of the three daughters he had with Jane Puleston came under serious doubt.

Regardless of the legal proceedings, Jane Puleston’s father, John Puleston, was not willing to give up the fight for his granddaughters’ inheritance. After Edward died in Dublin Castle, John Puleston raided Penrhyn with soldiers, trying to find a document that Rhys claimed proved he was the rightful heir. After years of litigation, the two sides agreed to divide the estate between Edward’s daughters and his brothers.

The estate was later inherited by Rhys’s son Piers Griffiths who is said to have been a pirate and to have built a secret tunnel between Port Penrhyn and the old house. Regardless of whether these stories were true, Griffiths gradually mortgaged parts of the estate until 1621 when Penrhyn was sold to John Williams.

John Williams became King James I’s chaplain in 1617, Bishop of Lincoln, Lord Keeper of the Great Seal, and Archbishop of York. He died without children and left the estate to his nephew Griffith Williams. Part of Penrhyn was later inherited by Ann Susanna Warburton who married Richard Pennant.

Gifford Pennant travelled to Jamaica in 1656 as a soldier in Cromwell’s Army. Here he bought sugar plantations and the family rose in social standing when his son, Edward, became the Chief Justice of Jamaica. The family returned to UK, where his eldest son, Samuel, became Lord Mayor of London while his other son, John was a successful merchant. With the money from the sugar plantations, John bought half of the Penrhyn estate with the other half bought by his son, Richard Pennant. He married Anna Susannah Warburton in 1765 and became the first Lord Penrhyn. As MP for Liverpool, Penrhyn was an outspoken supporter of rights for slave owners. In the 1780s, he commissioned Samuel Wyatt to update the medieval house. He also began to develop the slate quarry.

On Lord Penrhyn’s death in 1808, the Penrhyn Estate was inherited by his second cousin, George Hay Dawkins, who adopted the surname Dawkins-Pennant.  Dawkins-Pennant commissioned the architect Thomas Hopper to build a home that would reflect his status as a major landowner. Built in the Neo-Norman style, Hopper included features such as turrets, a tower and a keep. Hopper also designed Englefield House.

In 1840, the Penrhyn Estate was inherited by Edward Gordon Douglas through his marriage to Dawkins-Pennant’s elder daughter, Juliana. He was made 1st Baron Penrhyn of the second creation in 1866. He, and his son and heir George, continued to develop Penrhyn Quarry but were opposed to trade unions. This led to bitter strikes over union recognition and workers’ rights, culminating in the Great Strike of 1900–1903, the longest dispute in British industrial history. The family rarely visited the castle and was used mainly as a holiday home in the summer months. Visitors included Queen Victoria, her son Albert Edward, Prince of Wales and William Gladstone.

After Alan George Sholto Douglas-Pennant and his two eldest sons died in the First World War, the estate was left to his youngest son Hugh Napier. By 1949, much of the land was sold off, and the estate was neglected. Hugh’s niece, Janet Pelham inherited Penrhyn in the 1950s, and attempted to live here but found the castle too large to maintain and shortly after gave the estate to the National Trust.