Number 12 Merrion Square, was built between 1764 and 1766 for Sir William Brownlow. It is a beautiful house of considerable scale and presentation. Brownlow was a linen manufacturer and an MP for Lurgan, county Armagh from 1753 to 1794. In April 1764 the foundations for the house were laid. Over the next 2 years payments were made by Brownlow through a Mr Welldon to Wall the bricklayer, Morgan, stone carver, Gilliard, carpenter and Clement, bricklayer. 721 feet of window glass was provided by Turner and Lilly glass manufacturers of London. Over the period April 1764 and December 1765 £3,205 18s was spent on the house.
By the time Brownlow married Catherine Hall in 1765, the house was at an advanced stage of construction and after travelling in France the couple took up residence at Merrion Square in 1766. Number 12 is the largest of all the houses on the north side of Merrion Square and the interior is palatial in scale and decoration.
The single bay entrance lobby is exceptionally broad and tall and it is the only known hall in a terraced house in Dublin to have an Ionic pilaster order.