Grosmont remained a borough governed by mayor and coporation until the mid C19, and the Town Hall is a sign of its former importance during the medieval period. The present early C19 Town Hall was built on the site of the old one, which was timber-framed and much larger.
In 1828 The Duke of Beaufort offered to rebuild the market hall, which had fallen into disrepair. The new Town Hall built 1831-2 provided an upstairs assembly room, and a ground-floor market hall.
The external stone staircase on the W side, appears to have been added sometime after 1832, but there were few C19 changes. Bradney's 'History of Monmouthshire' includes a photograph of the Town Hall in 1904 showing the arcaded market hall open to the street on all sides. However, sometime during the earlier C20, the S end was enclosed. The Duke of Beaufort donated the town hall to the parish in 1902.

Source: Cadw Listed Buildings. ALH 05/03/2012