It dates back at least to the mid thirteenth century - it was recorded as part of the estate of Sir Adam de Basyng, one time Mayor of London. It passed on to John Mackworth, the Dean of Lincoln who in turn passed it on to the Dean and Chapter of Lincoln on his death in 1451. Three years later it was established as an Inn of Chancery - these were schools for law students before they passed on to an Inn of Court. Barnard's Inn along with Staple's Inn was linked to Gray's Inn Court. By the seventeenth century qualified attorneys were allowed to practice from Inns of Chancery as well as Inns of Court. By 1830 it had effectively become a set of residential chambers. In 1888 the link to the Dean and Chapter of Lincoln was broken and soon the it was purchased by the Mercers' Company to serve as premises for the Mercers' School up until 1959.
The buildings consist of the Hall, the 18th century chambers and reception room. The Hall dates from the 15th Century with 16th century panelling. There is also some chalk-and-tile walling in the seminar room which predates this.
Barnard's Inn was badly damaged during the Gordon riots of 1870. The distellery next door was owned by a Roman Catholic, Mr Langdale who escaped through the cellars when his building was set alight by rioters. The Hall and other buildings were damaged and one of the officers of the Inn witnessed a "sturdy fellow" pumping up gin from the cellar which he proceded to sell at a penny a mug to the thirsty onlookers of the fire. The Inn received £3,200 in compensation for the damage.
The Hall suffered from poor repair and two inadequate resorations in the nineteenth century. In 1932 the Mercers' Company organised substantial repairs to the roof and installed two fireplaces of Tudor design. The windows were reglazed, releded and reframed. They contain the armorial bearings of Principals of Barnard's Inn: