St James' Southbroom is a medium sized church, roughly square in plan which seats 250 comfortably and up to about 400 at festivals. The oldest part of the building is the fifteenth century tower, a grade I listed structure, one of the Westwood group, Similar towers can be found at Westwood, Yatton Kennel, West Kington and Nettleton. These towers are considered distinctive as a group in this country. F J Allen wrote 'the characteristic feature of all this group is the covering of the upper stage with window tracery of which only a small portion is perforated, while the tracery is sunk or recessed in rectangular frames. All the towers have panelled parapets and are of oolite from north Wiltshire.
St James' tower bears the scars of bombardments from Jump Hill by General Waller's forces in 1643. The cannon balls were found in the tower in 1780, their present whereabouts is not known. The tower houses a peal of six bells which are rung twice each Sunday.
Until 1831 the church was a chantry chapel to the parish of Bishop's Cannings. It is believed that at one time it was used as an isolation hospital, probably for a leper colony but the growth of Devizes in the early nineteenth century required another parish church and the old chapel was rebuilt as the Parish Church of Southbroom and Roundway..
The nave is square with a small sanctuary at the East end. There is no chancel. To the right of the sanctuary is the Vicar's vestry with a choir vestry to the left of the sanctuary, entered through a door in the NE corner of the nave.
The pulpit stands to the left of the sanctuary with the lectern to the right. The wooden pews are divided by a centre aisle and a line of three pillars midway along each side of pews supports the centre of the roof. Side aisles run East to West beside the walls. At the West end is a fine balcony, built in 1948, with choir stalls and pipe organ.
Around the walls are monuments to prominent local citizens prominent among which are tablets inscribed to the memory of the Coward family, late of Roundway Park. The walls and ceiling are painted white and together with the clear glass in the nave windows give a feeling of light and space to the building.
In the South East corner hang the battle standards of the Wiltshire regiment, laid up in this, the regimental church. Beside them on the South wall is the book of remembrance of the 1914-1918 war with the book of remembrance from the 1939-1945 conflict on the East wall of the nave, adjacent to the choir vestry door. Memorials to those who fell in earlier conflicts include the Indian Mutiny, New Zealand, China and the Zulu War.
Entrance to the church is by the West door, under the balcony. The area beneath the balcony is empty of pews and forms a meeting place after services. In the NW corner is an area of carpet and a set of small chairs and tables suitable for young children. The font stands in the SW corner beside one of the two staircases up to the balcony.