The current building was erected in 1724 and is at least the fourth building. It had earlier been the site of an Elizabethan court built in 1536, which was replaced in 1571 by a timber-framed construction. The timbers from the original building were used to construct the Shire Hall, which provided an open trading area on the ground floor with rooms above. The building, described in Buildings of Wales as "a mighty affair", is constructed of Bath stone ashlar and was designed by a little-known architect, Philip Fisher (d. 1776) of Bristol, at the cost of £1700. The Courts of Assize were transferred to the building in 1725, with the courtroom itself located on the first floor above the open arches used as a market area. Richard Watkins made the clock in the pediment in 1765.

The interior of the building was remodelled in 1828, and a new exterior stair tower with a glazed lantern was added, enclosing a grandiose new staircase. Thomas Hopper was involved with improvements to the Shire Hall under "Royal assent". He was involved in revisions to Penrhyn Castle, near Bangor, for many years. He and Edward Haycock, Sr., extended the Shire Hall building along Agincourt Street, creating a new staircase and larger courts. Hopper took up residence on Monnow Street in Monmouth while this was happening.

The sculpture of King Henry V, in a niche above the front entrance and below the clock, is generally considered to be of poor quality, variously described as "incongruous", rather deplorable", "decidedly-bad”, and "pathetic. Like a hypochondriac inspecting his thermometer". It was added in 1792 by Charles Peart, a professional sculptor born nearby English Newton. The inscription reads: HENRY V, BORN AT MONMOUTH, AUG 9TH 1387. The carved birth date is now thought to be incorrect.

Trial of the Chartist leaders

The County Gaol was located a short distance from the courtrooms. Here, the Chartist leader Henry Vincent, who had sought the right of all men to vote in parliamentary elections, was imprisoned before being tried at the assizes. Vincent was convicted, but the unpopularity of the verdict led to protests that eventually led to miners being killed in a clash with the military at Newport on 4 November 1839. John Frost was arrested in Newport shortly after the riot, followed by other group leaders. A Special Commission opened at Shire Hall on 10 December 1839, and an appointed Grand Jury considered what charges to bring against them. The Grand Jury included Lord Granville Somerset, brother of the Duke of Beaufort; John Etherington Welch Rolls; Octavius Morgan; and four Members of Parliament, Joseph Bailey, William Addams Williams, Reginald James Blewitt, and Sir Benjamin Hall. Frost, William Jones, Zephaniah Williams and five others were duly charged with high treason, and their trial began on 31 December. It has been described as "one of the most important treason trials in the annals of British law." The judges were the Lord Chief Justice, Sir Nicholas Tindal, Sir James Parke, and Sir John Williams. He was notorious for sentencing the Tol Puddle Martyrs to transportation in 1834. Counsel for the Crown was the Attorney General, Sir John Campbell; Frost's counsel was Sir Frederick Pollock.

While the trial took place, measures were taken to protect Monmouth against Chartist insurgents. Troops were billeted at the White Swan, and some were stationed at the gatehouse on the Monnow Bridge. Granville Somerset and Benjamin Hall spoke in Frost's defence. In sum, Lord Chief Justice Tindal drew attention to the certainty needed for a conviction, suggesting his desire for an acquittal. All eight men were found guilty, but the jury recommended mercy. On 16 January 1840, the judge sentenced Frost, Jones and Williams to be hanged, drawn and quartered; they were the last men in Britain to be sentenced to that punishment. The other five men were sentenced to transportation. On the day before they were due to be executed, 29 January, the Cabinet under Lord Melbourne took Lord Chief Justice Tindal and asked Queen Victoria to reduce all the sentences to transportation. On 2 February 1840, the prisoners were escorted to Chepstow and put on the steamer Usk for Portsmouth, where they were transferred to the ship Spithead with over 200 other prisoners and taken to Van Diemen's Land.