Richard Cassels, who originally trained as an engineer, came to Ireland in 1728 at the behest of Sir Gustavus Hume of County Fermanagh to design for Hume a mansion on the shores of Lough Erne. Hume had probably discovered Cassels working in London where he was influenced by the circle of architects influenced by Lord Burlington. Cassels, soon after arrival in Ireland, established a thriving architectural practice in Dublin. Architecturally at the time Dublin was an exciting place to be – Edward Lovett Pearce, also newly established in the city, was working on Castletown House, the great mansion of Speaker William Connolly, and the new Irish Houses of Parliament simultaneously. Both of these buildings were designed in the newly introduced Palladian style. Palladian architecture was currently enjoying a revival that was to sweep across Europe and be adopted with a fervour in Ireland. Cassels was well versed in the concepts of Palladio and Vitruvius, but was also sympathetic to the more Baroque style of architecture.
In Dublin itself, Cassels worked on the Houses of Parliament with Pearce, his mentor and friend. Cassels' first solo commission was the
Printing House of Trinity College, designed to resemble a temple complete with a doric portico. This portico was an interesting feature symbolising Cassels' early work – a portico is an almost essential feature of Palladian architecture. But as Cassels' work matured he tended to merely hint at a portico by placing semi-engaged columns supporting a pediment as the focal point of a facade. Perhaps he felt the huge Italian porticos that provided shelter from the sun were not requisite for houses in the less clement Ireland. This blind, merely suggested, portico is a feature of his final Dublin masterpiece Leinster House built for the Earl of Kildare between 1745 and 1751. In 1741 he designed the Bishop's Palace which is now part of Waterford Treasures - Three Museums in the Viking Triangle, Waterford, Ireland. A comparison of the Printing House and Leinster House shows the evolution from the true Palladian style to the, commonly referred, Georgian style in Ireland during the quarter century that Dublin was to be almost rebuilt.
The untimely death of Edward Lovett Pearce, aged 34, in 1733, made Cassels Ireland's leading architect working in the sought after Palladian style. He immediately assumed all of Pearce's commissions and thus began designing a series of lavish country houses. Following the completion of the Houses of Parliament there seemed to have been a rush by the aristocracy to build a series of new town houses in the same style and Cassels was often the first choice for architect. This led to the creation of what came to be known as Georgian Dublin.
For his exteriors he used a Palladian style that was distinctive for its strength and sobriety. In this he seems to have been influenced by Pearce and also James Gibbs. However, when it came to interiors, Cassels gave full rein to his love of the more continental Baroque. Walls were covered in stucco reliefs, ceilings medallions and motifs of plaster, segmental mouldings, and carvings, in an almost rococo style peculiar to Ireland.