St Mark's is the only civic church in the country and the chapel had originally served the Hospital of the Gaunts. It was surrendered at the Dissolution and purchased by the Council in 1541, becoming known as the Mayor's Chapel. It was not called the Lord Mayor's Chapel until 1899, when the office of mayor was elevated by Queen Victoria. Park Street, behind, was altered later in the 19th century and the hollow at its junction with Frog Lane and Frogmore Street was bridged to improve the gradient. This had been anticipated when Park Street was first laid out and the houses at the bottom had high basements and flights of steps.

The Gothick porch at St Mark's had been added in the late 1770s. The great west window above it is not the original for there were substantial restorations at the chapel in the 1820s. The window was removed and this copy installed while the original was purchased by Henry Brooke of Henbury Hill House who 'set it up in a sham ruin on Henbury Hill to serve as an object from his house' (G W Braikenridge). It still exists today, off the Ridgeway, very close to modern housing. Compare with Simon Waters's photograph from 2001, K6083.