In 1695, the harsh Penal Laws were introduced in Ireland and came in full effect by the early 18th Century, which had a disenfranchising influence on the Catholic and Presbyterian Irish populations. Ireland was experiencing the Protestant Ascendancy, which began in the 17th Century and ended in the 19th Century. Landowners from the Church of England, as well as clergy from the Church of Ireland and the professional class, were dominating the country during this time, with the city expanding greatly. In 1700, Dublin was the second largest city in the British Empire, with over 60,000 inhabitants and houses modernised along the Liffey riverfront.

In the beginning of the 18th Century, Dublin was still in the Middle Ages, in terms of layout. However, it underwent major renovations, with narrow streets replaced by wide Georgian-style streets. Today's O'Connell Street, formerly Sackville Street, was changed in this manner. Five important Georgian squares were designed, as well as many monumental Georgian buildings erected. Initially, the north side of the Liffey was the domain of aristocrats, but they gradually came to favor the south side and the huge mansions on the north side became tenements occupied by the poor. The only areas that retained the medieval layout were Temple Bar and around Grafton Street. The influence of the 8th-century 'Enlightenment' was not without problems. It was rife with gang wars and other forms of violence. Citizens organised demonstrations outside the parliament, when it passed unpopular laws. The revolutionary United Irishmen movement planned an unsuccessful uprising in Dublin in 1798 as well.

In 1801, Great Britain and Ireland merged to form the United Kingdom of Great Britain and Ireland, under the Irish Act of Union. In turn, Ireland lost its Parliament and most of its political influence. Dublin continued to expand but suffered tremendous financial loss. Many of the finest mansions, such as Aldborough House, were put up for sale within a few years and the elegant Georgian neighborhoods were turned into slums. Eventually in 1829, after mass rallies, Irish Catholics regained citizenship of the UK.