St Boniface Old Church is situated in The Undercliff area of the island, a short distance inland from the S coast. The church consists of a nave, chancel and a S porch leading to a Romanesque doorway. The chancel has N and S lancet windows. The chancel arch was formerly a simple round headed arch. The neo-Norman appearance of the chancel arch is due to restoration work carried out in the early 20thc by Percy Stone (Lloyd and Pevsner 2006, 86-7).

Domesday Book records that in 1066 'Bonecerce' was held by Estan of Bonchurch and Earl Godwin; in 1086 its lordship passed to William (son of Azur). The manor valued £1. The church of St Boniface is alleged to have obtained its dedication from a visit of the 8thc missionary to Germania (Cox 1911, 39) and there is a tradition that the church was built by monks in the 8thc (Renn 1969, 266). However, the dedication may be due to the mistaken belief of an association with Boniface because of the place-name (Gelling 1981, 7) or the acquisition of the saint's relics at a later date. The Domesday Survey place-name 'Bonecerce' indicates the presence of a church by 1086 and can be interpreted as "Bana's church", a church built by a murderer (Old English Bana) as an act of atonement (Ekwall 1960), or "Buna's church" (Gelling 1981, 7). A re-evaluation of the place-name reverts to the traditional interpretation, with Bonchurch probably meaning 'the church of Bona', from Old English 'cirice' and an Old English personal name which may be a short form of the Latin name Bonifatius, i.e. Boniface (Mills 1996, 31). Sir John Oglander stated that the church ‘was erected in ye reygne of William ye Conquerer by one Johannes de Argentine ... [who] got itt to be made a p’risch, by means of his brother’s sonn, Walkelyn, then Bishop of Winchester’ (Stone 1891, II, 11).

The small church here at Bonchurch was originally even smaller, as witnessed by the side alternate quoin in the N wall of the nave about a third of the way along from the W end, now forming a straight joint in the fabric. The Romanesque S doorway, approximately in the middle of the present nave S wall, would have provided access to this smaller nave. The thickness of the nave S wall at only 62 cm may suggest Anglo-Saxon workmanship, whereas the S doorway with chevron ornament would indicate a date within the 12thc. This leads to the hypothesis that the doorway was possibly inserted into an earlier structure.