There are varied accounts as to when exactly the main tower/keep was constructed; ranging anywhere from the 13th century to the late 15th century, but most likely around 1250 CE. It was built by the O'Bannon clan and was originally called "Léim Uí Bhanáin" (as was the fertile land around the castle which was associated with the Bannon clan), or "Leap of the O'Bannons". The O'Bannons were the "secondary chieftains" of the territory and were subject to the ruling O'Carroll clan. There is evidence that it was constructed on the same site as another ancient stone structure perhaps ceremonial in nature, and that that area has been occupied consistently since at least the Iron Age (500 BCE) and possibly since Neolithic times.
The Annals of the Four Masters record that the Earl of Kildare, Gerald FitzGerald, tried unsuccessfully to seize the castle in 1513. Three years later, he attacked the castle again and managed to partially demolish it. However, by 1557 the O'Carrolls had regained possession.
Following the death of Mulrooney O'Carroll in 1532, family struggles plagued the O'Carroll clan. A fierce rivalry for the leadership erupted within the family. The bitter fight for power turned brother against brother. One of the brothers was a priest. While he was holding mass for a group of his family (in what is now called the "Bloody Chapel"), his rival brother burst into the chapel, plunged his sword into him and fatally wounded him. The butchered priest fell across the altar and died in front of his family.
In 1659, the castle passed by marriage into the ownership of the Darby family, notable members of whom included Vice-Admiral George Darby, Admiral Sir Henry D'Esterre Darby and John Nelson Darby. During the tenure of Jonathan Charles Darby, séances were held in the castle by his wife Mildred Darby who was a writer of Gothic novels: this led to publicity about the castle and its ghosts. The central keep was later expanded with significant extensions, but in order to pay for these, rents were raised and much of the land accompanying the castle was sold. This is one theorised motivation for the burning of the castle during the Irish Civil War in 1922.
In 1974 the castle was bought by Australian historian Peter Bartlett, whose mother had been a Banon. Bartlett, together with builder Joe Sullivan, carried out extensive restoration work on the castle up to the time of his death in 1989.
Since 1991, the castle has been privately owned by musician Seán Ryan, who is continuing the restoration work.
A Red Lady ghost is reported to walk the halls holding a dagger. The castle has been visited by paranormal investigators from ABC Family's Scariest Places on Earth and Living TV's Most Haunted in its first season, as well as The Atlantic Paranormal Society (TAPS) from Syfy's Ghost Hunters. Most recently in August 2014, Travel Channel's Ghost Adventures filmed their tenth season Halloween special at the castle. The castle is allegedly haunted by a sinister elemental spirit referred to only as the, It. 
Rebuilding estimate of 1922
After its destruction Mr Darby obtained a reinstatement estimate from Beckett & Medcalf, surveyors in Dublin, that was issued in September 1922. Confusingly, it gives the address as Leap Castle, Roscrea, Co. Tipperary. The net "Amount of Claim" was £22,684.19.1, equivalent to about €1m in 2018. The claim was settled for a lesser amount.
- Leap Castle Archived 2012-05-05 at the Wayback Machine
- Bartlett's biographical materials, including Leap Castle restoration details - National Library of Australia
- Lockdown Your October with Ghost Adventures
- Hit American show Ghost Adventures filming in Ireland
- Simon Marsden
- Haunted Britain
- Irish Culture and Customs (Last listing)
- Description, history and pictures of Leap Castle