St Margaret's has an aisleless nave, chancel and round W tower. The nave and chancel are rendered; the nave thatched and the chancel roofed in tiles. There is a 12thc. window in the N chancel wall. The nave has a 12thc. S doorway under a later porch and a 13thc. N doorway, now blocked. The flint tower is of two storeys, the upper rendered. There are small round-headed lancets in the lower storey; two on the N side, two on the S and one on the W. The upper storey has 12thc. double bell openings in the cardinal directions, alternating with plain round-headed windows of brick with chamfered jambs. 12thc. features described here are the S nave doorway and the bell openings of the tower.

In 1086 Herringfleet was among the king's lands kept by Roger Bigod. Previously it had been held as a manor by Wulfsige. No church was recorded at that time. The manor was afterwards held by Catharine fitz Osbert, and in the reign of King John was held by Roger fitz Osbert. Inc.1216 he founded a priory of Augustinian canons dedicated to SS Mary, Olave and Edmund at the NW end of the parish, by a ferry crossing of the river Waveney, that formed the Norfolk border. The priory was given land at Tibenham and later the churches of Witlingham, Herringfleet, Burgh Castle and Hales, among others. Meanwhile, the Domesday manor subsequently passed to the Titshall family and by 1275 to the de Loudhams.

Benefice of Somerleyton, Ashby, Fritton, Herringfleet, Blundeston and Lound.

The bell-openings have the chamfered block capitals seen at Henstead and Ilketshall St Andrew, and the use of a billet label extending down the jambs can be compared with the S doorway at Westhall and the N doorway at Wissett. Westhall also has chip-carving on its W doorway (though not on the imposts). The tower is called very early Norman by Cautley, and Norman by Pevsner, who notes that the triangular heads of the bell-openings are more normally found in Anglo-Saxon work. The E bell-opening in particular looks Anglo-Saxon on account of the flanking pilaster strips. A date in the 1080s or '90s is suggested for this work. The S doorway must be later, on account of the chevron ornament, but the chip-carving would be unlikely afterc.1140, so a date in the 1130s is suggested.