86 St James's Street is a Crown property and Grade II listed. At the time of its construction between 1862 and 1865, the building was described as "High Victorian".

The property consists of seven levels, including the lower ground floor and basement. On the ground floor, it features four arched bays. The right-hand bay, at the top of a flight of stone steps, provides the main double-doorway entrance. The windows on the first and third floors are arched, including the four stone dormer windows on the top floor. Above the steeply pitched slate roof, two tall rustic banded chimney stacks stand on each side. The main entrance leads to a panelled hall and a freestanding staircase constructed from stone steps, with an open well and a cast-iron ornamental balustrade. There are three large rooms on the ground floor, two of which are used as Masonic temples, while the third serves as a Board Room. On the first floor, there is a front dining room overlooking St James's Street as well as St James's Palace. The rear areas on this floor are used for dining and daytime meetings. On the second floor, there is a licensed bar at the front, while the rear areas house two additional Masonic temples. The third floor contains three dining rooms and two more Masonic temples. The fourth floor is occupied by offices. The seven Masonic temples, named Grand Temple, Brazil, Bristol, Hong Kong, River Plate, Warwickshire, and Johann Gutenberg, were all dedicated on 30 September 1980.

The site of 86 St James's Street has been used for public houses and private clubs since the early 18th century. In 1702, the building was home to Williams' Coffee-House, a popular venue for the literati of the day. In 1749 the premises became a tavern. Following several other landlords, Richard John Atwood took on the lease in 1774 and ran the premises as a coffee house and a club. In 1772 he established a club called Atwood's which counted the historian and freemason Edward Gibbon among its members. In 1785 the house caught fire and was destroyed, but was rebuilt the following year. 

By 1801 the house at 86 St James's Street had become a public house, and was advertised as a place “where gentlemen meet on purpose to play at Billiards”. After 1817 the Union Club was based here until the pub closed down in 1820, when the premises were taken over by Carey’s, the map makers. In February 1862 the building was demolished following a successful application to the Commissioners of Woods and Forests to erect a new building for a club House and chambers.

The present building at 86 St James's Street was built between 1862 and 1865 following a design by Sir James Thomas Knowles (1831-1908). From 1866 to 1869 it was occupied by the Civil Service Club with residential apartments on the upper floors. In 1870 the Thatched House Club became the occupiers of the premises and remained here until 1949. In 1950 the lease of 86 St James's Street was taken over by the Union Club, previously housed at 10 Carlton House Terrace which had been taken over for government use. In 1964, the Constitutional Club took over the lease and carried out extensive refurbishment. On 03 December 1977, The Grand Lodge of Mark Master Masons of England and Wales obtained a lease for a term of 99 years. The conversion works began on 18 February 1978 and were completed by July 1979. Mark Masons’ Hall was formally opened on 01 September 1979.