After purchasing Lismore he made it his principal seat and transformed it into a magnificent residence with impressive gabled ranges each side of the courtyard.

The principal apartments were decorated with fretwork plaster ceilings, tapestry hangings, embroidered silks and velvet.

Lismore featured in the Cromwellian wars when, in 1645, a force of Catholic confederacy commanded by Lord Castlehaven sacked the town and castle.

The castle (along with other Boyle properties – Chiswick House, Burlington House, Bolton Abbey and Londesborough Hall) was acquired by the Cavendish family in 1753 when Lady Charlotte Boyle (1731-1754), the daughter and heiress of the 3rd Earl of Burlington and 4th Earl of Cork, married the Marquess of Hartington, who later became, in 1755, the 4th Duke of Devonshire (1720-1764), a future Prime Minister of the Kingdom of Great Britain.

Their son, the 5th Duke (1748–1811), carried out improvements at Lismore, notably the bridge across the River Blackwater in 1775 which was designed by Cork-born architect Thomas Ivory.

Lismore was always the Bachelor Duke's favourite residence, but as he grew older his love for the place developed into a passion.

Pugin, were commissioned to transform the ruined chapel of the old Bishop's Palace into a medieval-style banqueting hall, with a huge perpendicular stained-glass window, choir-stalls and Gothic stenciling on the walls and roof timbers.

The chimney-piece, which was exhibited at the Medieval Court of the Great Exhibition of 1851, was also designed by Pugin (and Myers) but was originally intended for Horsted Place in Sussex; it was rejected because it was too elaborate and subsequently bought for Lismore – the Barchard family emblems later replaced with the present Irish inscription Cead Mille Fáilte: 'a hundred thousand welcomes'.

Under Lord Burlington the planting has been enhanced, and contemporary sculpture added, including works by Sir Antony Gormley, Marzia Colonna and Eilís O'Connell.