In 1408, the Dean recorded that it had three chantries: one dedicated to the Blessed Virgin Mary, probably where the organ now stands, was founded by Lucy Clyfton in 1305; St Katherine’s Chantry in the south transept, founded in about 1316 by William Mounte; and the Hungerford Chantry, in the north transept, probably dating from 1441 and endowed by Walter, Lord Hungerford, who fought at Agincourt and became Treasurer of England in 1428. It was also in his name that the Hospital of St John, Heytesbury was endowed. Only the screen remains from his chapel which must originally have had a remarkable fan-vaulted ceiling. He and several other Hungerford family members are buried in Salisbury Cathedral or at Farleigh Hungerford Castle, but the remains of a tomb, probably that of the later Sir Walter, a member of Henry VII’s council, who died in 1515, his wife and perhaps his son, can still be seen in the Hungerford Chapel. Another Walter Hungerford, an adherent of Henry VIII’s chief minister, Thomas Cromwell, was made 1st Baron Hungerford of Heytesbury, and resided in Heytesbury House. He fell from grace, however, with his patron Cromwell, was arrested at Heytesbury and, in 1541, beheaded, his lands, including those at Heytesbury, being forfeit to the Crown. Thus ended the illustrious Hungerford family’s connection with Heytesbury which had begun in the early 12th century. The estate then came into the hands of the Moore family and the alabaster effigies of Thomas Moore, High Sheriff of Wiltshire, who died in 1623, his wife, Rachel, and child, damaged by order of the Dean of Salisbury in 1673 for reasons unknown, can be seen, together with a plaque inscribed with a rather charming contemporary acrostic, in the north chancel aisle. In 1641, the Moores sold the Estate to the Ashes and, through them, the à Court family became Lords of the Manor of Heytesbury until 1933, when the estate was sold to the World War I poet, Siegfried Sassoon. The walls of the Hungerford Chapel are adorned with à Court family memorials.By the mid-19th century congregations had dwindled, like many others at the time, and the church had fallen into a sad state of neglect. It was divided in half by a solid wooden screen extending from north to south, west of the crossing, leaving only the nave available for normal worship. Here, the box pews faced west and the high pulpit, with its adjoining clerk’s desk, lectern, prayer desks and stalls were all at the west end. A small door through the screen under the western arch of the crossing gave access to the vestry in the north transept, and to the Hungerford Chapel, although this was closed off and used for à Court family burials (the coffins were moved to a purpose-built mausoleum in the south-west corner of the churchyard during the 1865-67 restoration). A second door gave access to the chancel, with its ancient wooden stalls facing east and inwards, used only for occasional celebrations of Holy Communion. The chancel aisles, which may already have fallen into ruin, had been demolished, presumably to save money. In the nave, upper galleries provided seating for Lord Heytesbury and his family, together with, to one side, seats for the twelve men (dressed in their scarlet cloaks or, later, blue overcoats) and one woman of St John’s Hospital, and to the other, for the children of the school run by the Custos of the Hospital. The organ also stood at the west end of the upper gallery.

From this sorry state of neglect the Church was rescued, in 1865–67, by William Butterfield, the well-known Gothic revival architect and member of the influential Oxford movement, who by removing the dividing barrier between the chancel and the nave, opened up the interior. He also removed the upper galleries in the nave and the high pulpit. The west facing box pews were replaced by the present open, east facing pews and a new pulpit and font were provided. The arches of the blocked up chancel aisles were re-opened and the aisles themselves re-built. Extensive repairs were carried out to the rest of the church. The quality of Butterfield’s work is evident from the fact that the slated roof slopes, laid during his restoration, have lasted nearly 150 years, some 70 years longer than could normally have been expected. On the other hand, Butterfield managed to persuade the then Lord Heytesbury, the incumbent and churchwardens, to accept his signature geometric tile decorations which, contrary to his claims, have no relationship with medieval church interiors and are not to everyone’s taste!

The Warminster Journal devoted a whole page to the opening ceremony following the restoration, which took place on 10th September 1867. A service, led by the Bishop of Oxford, accompanied by the Bishop of Salisbury, was held in the church at 12.30 pm, followed, at 4.00 pm, a lunch for 350 people. Many of the guests attended a second, evening service, after which, at 7.00 pm, 400 of the working poor sat down to a supper provided by the church wardens.

Despite this very comprehensive restoration, a number of early features remain. The east end, with its tall, single lancet window and slim Purbeck marble pillars, reminiscent of ‘the new’ Salisbury Cathedral, with which it may have shared a master builder, is the earliest part of the Church and remained more or less untouched by Butterfield who admired it greatly. The north and south arcades in the chancel date from c.1185 and in the south wall of the sanctuary is a 13th century piscina. The arches in the north and south chapels are from the 15th and 13th centuries respectively whilst the nave arcades, partly re-built and with new bases, date from the 14th century. The clerestory was added in the middle of the 15th century.

The famous antiquarian, William Cunnington, lived for 33 years in the Old Estate House in Heytesbury from c. 1775 until his death in 1810. He is buried in the churchyard. His friend and patron, Sir Richard Colt Hoare, after visiting the church in the 1820s, described it in its depleted state (History of Modern Wiltshire, The Heytesbury Hundred).

The church has a remarkable and very fine organ, provided second-hand in 1854 by the London firm of J.W. Walker, as a gift from Mr John P. Prangley of Heytesbury. It came from St Mary's Church, Bermondsey, and has been attributed to Gerard Smith, who was active between 1689 and 1725; certainly much of the pipework dates from that period. It was conservatively reconstructed by J.W. Walker during the 1865-67 restoration at a cost of £160, when it was fitted with new casework and re-installed in its present position at the head of the south chancel aisle. It has not been significantly altered since then. Its outstanding value has been recognised by the award of a Grade I Historic Organ Certificate by the British Institute of Organ Studies.

The church also has a fine ring of six bells, the oldest and largest being the tenor, weighing 191/2 cwt , cast c.1460, whilst the remaining bells range in age from 1619 to 1843, the smallest weighing 8 cwt.

There are two memorial tablets of particular interest inside the church. One is in memory of David Williams, founder of the Sunday School movement and vicar of the parish from 1795 to 1836, whilst the other commemorates the antiquarian, William Cunnington.

In 1967, a restoration project marked the centenary of the earlier restoration. The wagon roof of the nave was coloured pale blue and the 80 carved bosses, one at the end of each beam and the rest on the horizontal beams at its base, were picked out in white, blue, scarlet, yellow and green. The walls were lime washed white and most of the tiles cleaned. In 1983 the church was re-wired and wrought-iron pendant lights, which had previously hung in Salisbury Cathedral, were installed.