Brackley is a town in the far S of the county, sited in a loop of the Great Ouse, which forms the border with Buckinghamshire. It is an ancient site on the main road from Northampton to Oxford, and evidence of Iron Age and Roman settlement has been found in the town. There seem to have been two centres to it; one around St Peter's church towards the E of the present town, and the other on its southern edge, overlooking the river, around the site of the Norman castle, of which a motte 3m high and 40m in diameter survives.

St Peter's has an aisled and clerestoreyed nave, the N aisle gabled and wider than the S, which has a lean-to roof. The four-bay arcades differ in date, the S being 13thc. and the N 14thc. Both arcades have long responds at the E end, pierced by smaller arches. This unusual arrangement must be related to the lost 12thc. transept, because part of the N impost of the W crossing arch (or possibly a section of stringcourse) survives in the N arcade wall at this point. Also from the 12thc. nave is an elaborate S doorway, now set in the aisle. This is accessible through the modern church hall that has been added to the S side of the nave. The chancel is 13thc., but heavily restored c.1885. It has a heavily restored 14thc. S chapel, two bays long. N vestry was added c.1885. The glory of the church is its W tower, mid-13thc. in its three lowest stages with a late-medieval fourth storey. The lower part is decorated with full-sized figures in niches, wall arcading in the bell storey and an elaborate W doorway with stiff-leaf capitals. Construction is of grey stone rubble. The new church hall is of yellower rubble, incongruously provided with triangular-headed windows and doorway. The church was restored by C. J. Bather c.1873, and further by J. O. Scott c.1885, when the vestry was added.

In 1086 both a church and a priest were recorded at Brackley. The church was included in the foundation gift to the Augustinian Abbey of Delapre (Leics) of the Earl of Leicester. This was in 1143. The present dedication, dating from 1884, reflects the former Chapel of St James (now destroyed), which appears to have originated as the chapel to Brackley castle, and to have been in existence in the 12thc. It still existed in 1791 (Bridges) but stands no longer. It should not be confused with the chapel originally belonging to the Hospital of SS James and John, which is now the chapel of Magdalene College School.

RCHME Report dates both the S doorway and the fragment of stringcourse to c.1175. The running scroll on the latter is almost identical to one on the font at Magdalene College Chapel, Brackley, which also includes dogtooth ornament and probably dates from c.1190-1200. There is nothing to connect the doorway at St Peter's to work at Magdalene Chapel, however, and a date in the 1170s is acceptable for this.