The church has chancel, nave with N and S aisles and N porch, and W tower with a vestry attached on the S. The church was rebuilt by William Butterfield in 1870-72. Some parts of the older stucture were retained. The S aisle is 14thc., the first two stages of the tower are 12thc. and the uppermost stage 14thc. The round-headed tower arch has a chamfered impost, but is otherwise plain. A round-headed window, deeply splayed, survives on the S face of the lowest stage of the tower and now opens onto the vestry. On the exterior the second stage windows of S, E and W faces (the E window is covered by the chancel roof and the W is partially hidden behind the church clock) have a continuous thick roll with inverted cushion bases (partially restored). The church walling is coursed rubble. There is some herringbone masonry visible in the tower walling. Romanesque sculpture is found on a reset fragment in the N aisle. The fragment is not from the church.

A priest at Barley is mentioned in DS as being among the tenants of Harduin de Scales, who held land there. VCH records that the advowson appeared to be in the gift of the tenants. In 1268 it was given to Chatteris Abbey, Cambridgeshire.

The church guide, when refering to a cross in the N aisle mounted on a Roman tile from St Albans, notes that 'nearby are other stones from that edifice'. Although this seems a rather oblique reference, the carving is in fact identical to carved jambstones on the S transept doorway of St Albans cathedral and is probably one of the original jambstones from that doorway. Comparisons may also be made with the so- called 'Aylesbury group' of fonts, in Buckinghamshire, in particular the rim decoration of the font at St Mary, Weston Turville.