Her most notable building was Townley House. In the 1770s, Mary married James Townley, a proctor. The couple established themselves in Ramsgate the east of Kent which was developing as a small port.
They included barracks, later converted into houses, the development of Albion Place in the centre of Ramsgate, but above all Townley House (1792), a large mansion considered to be an architectural gem.
A set of townhouses she designed in 1820 became the Regency Hotel and later included a language school. The building has recently been fully restored.
An account written by her relative and tutor, the artist Sir Joshua Reynolds, praises Mary Townley"s flair for architectural design, making her unique among women of her day. Mary Townley played a prominent role in local society, arranging balls at Townley House and entertaining the nobility.
Among her guests in the 1820s was King William IV.