A C11 church was extended around 1200 and a parallel nave was added in the mid-C13, when it became the church of a nunnery, parts of which still stand.  There was a drastic restoration in 1876-77.

Easebourne gave its name to the hundred in which it lies and the church may have been a minster (VCH 4 p53).  Midhurst, of which it is now effectively part, was originally a chapelry in the parish.  Its early history has recently been reassessed and though there was already a church, its position was changed around 1216, when a college of priests was established.  This served not only Midhurst but other chapels such as Fernhurst and Lodsworth (5 p113).  Around 1240 this was transferred to the Benedictine nuns of Rusper (by Horsham) (ibid p115) and became a subsidiary house.  By the time of its dissolution in 1536, it had become, under circumstances that are unclear, a house of Augustinian Canonesses.  The various occupants during this period used and extended the church. 

The south wall of the church is C11, for it has some repointed herringbone masonry and a tall, narrow round-headed doorway (blocked).  The doorway, despite its proportions, is post-Conquest.  A north aisle and tower were added around 1200, as the style would suggest, or possibly a litle later after the college of priests was founded.  The aisle no doubt had a lean-to roof, though nothing remains except for some of the west wall, beneath C19 refacing, and one and a half bays of a three-bay arcade.  The broad double-chamfered arches are pointed and the octagonal pier has a scallop-capital.  On the west respond is a corbel for the inner order of the arch.  The unbuttressed tower, though altered, keeps its original small openings; the lower ones round-headed and the rest pointed, like the plain chamfered tower arch and the west doorway.

The north aisle was replaced by a parallel nave, probably after the the nuns came.  The arrangement was less usual in churches shared by a religious house and a parish than that exemplified by Boxgrove, where the parish used the nave and the chancel was monastic.  The new nave for the parish is gabled and as wide as the existing nave.  The Burrell Collection drawing and Adelaide Tracy (I p113) show it had lancets - one rere-arch survives.   At the same time, the nuns extended their choir into the eastern part of what was now the south nave and to ensure separation replaced the east bay and a half of the arcade by a wall.  They rebuilt the chancel, which became possibly twice as long as now, with a square east end (4 p99).  It stood south of a parish chancel, the details of which are unknown – Quartermain ((W) p93) shows a low, east extension of indeterminate date.

Little more than windows were altered during the later Middle Ages.  The south side abutted onto the cloister and thus only had windows high up.  The Burrell drawing shows a four-light square-headed one, which looks C15 like the panelled tracery of the former west window of the parish nave, which is shown by Adelaide Tracy.  This was moved in the C19 to the south side (BAL MSS/DB 6/3/1) and keeps its old head.  A retooled moulded arch with semi-octagonal responds between the two chancels may be connected with a bequest by Sir David Owen in 1529/30 (see under monuments below) for alterations to the nuns’ choir, the prime purpose of which was to allow them to enter unseen from the convent (SRS 42 p100), though from the form it could also be C15.

After the dissolution, the parish used both naves.  In the C18 the nuns’ choir was a funerary chapel for the Montagues of Cowdray (3 p6) and was roofless by 1830, after which E Blore (Colvin 4th ed p133) rebuilt it in shortened form in 1834-36.  The parish chancel shown by Quartermain could date from then.  At some time, under-sized pinnacles were placed on the tower.

The present appearance of the church is due to Sir A W Blomfield’s restoration in 1876-77.  The specification of work (BAL MSS ibid) reveals that he virtually rebuilt the north nave and chancel with lancets, restored the arcade to three bays and replaced the south windows.  All roofs were renewed and the south chapel of 1830 was remodelled with a new east window.  The north chancel has much arcading and shafting and a new chancel arch.  A plan to heighten the tower with a taller spire was dropped, though the present one differs from the shingled one in the Sharpe Collection drawing (1804).  Finally, Blomfield refaced almost everything except the north and west sides in unattractive, rough stone.  Sir A Webb refaced the north side in 1912, at the expense of Lord Cowdray (3 p15), but his work differs hardly from Blomfield’s.  A plan to treat the west end similarly was frustrated by World War I.

There were repairs by S Roth in 1952-53 (ICBS).

Conventual buildings

The conventual buildings lay around a cloister south of the church.  The east range, now a house, is at right-angles to the chancel.  Though the nuns did not have their own church, their buildings were impressive, to judge from what is left.  The west front of the main house incorporates a triple chapter house entrance of c1270 with moulded arches and complex piers incorporating marble shafts.  Despite restoration - the marble shafts are renewed and the Burrell drawing shows the openings blocked - the quality is higher than anything in the church.  South of this a round-headed arch leads to a passage.  The upper storey containing the dorter was renovated in the C15 with one- and two-light square-headed windows.  Along the south walk of the cloister is the refectory, which has early C14 south windows of Y-tracery, now renewed.  There were almost certainly originally four not three, since the Burrell drawing shows a large opening with double doors where the long gap between the second and third windows now is.  The structure was later used as a barn (Hussey p223), for which the opening was made, and today is a parish room.  Only a wall marks the position of the west range.

Fittings and monuments

Font: The usual C12 square bowl, arcaded on three sides and with renewed shafts. 
Glass:
1. (East window) Heaton, Butler and Bayne, 1877 (CDK 1880 pt2 p121).
2. (North chancel) Heaton, Butler and Bayne, 1879 (www.stainedglassrecords.org).
3. (North nave, first window) H T Bosdet, 1894 (signed).
4. (North aisle, west window) Heaton, Butler and Bayne, 1877 (ibid).
Monuments:
1.  (North nave in reset C13 cusped recess) Sir David Owen (d1535).  He was the owner of Cowdray, a natural son of Owen Tudor and thus uncle to Henry VII (Visitation of 1530 etc p94).  His armoured alabaster effigy is conservative for the date of death.  In fact, it was made long before, for in his will of 1529 Owen directed it should be re-gilded (1 p33).  Originally there is said to have been also an effigy of his wife (ibid).
2.  (South chancel) Sir Anthony Browne, later First Viscount Montague (d1592), attributed to G Johnson (A White (WS 61) p68).  The Brownes bought Cowdray from Owen.  This monument was originally in Midhurst church and free-standing, but was brought here in 1851.  As there was less room, it was re-arranged, with Lord Montague kneeling behind and above the two recumbent effigies of his wives, instead of having a wife on either side (3 p14), with obelisks at the corners.  The original arrangement resembled Johnson’s monument to the Earls of Southampton at Titchfield, Hampshire (A White p65) - Montague’s daughter was married to Henry, Earl of Southampton (Visitation of 1530 etc, p84).
3.  Elizabeth Poyntz (d1830) A seated female figure by Sir F Chantrey.  It was ordered in 1832 (M Brown p272), so Gunnis’s suggestion (p95 - not repeated in Roscoe) that it was possibly made in 1814 is erroneous.  She was the last surviving Montague.
4.  William Poyntz (d1840) Her husband, by the Italian R Monti.  It was made in 1848 (Roscoe p840 as 'Eastbourne') and deliberately intended to match his wife’s monument.
Reredos: Stone showing the Last Supper and doubtless by Blomfield.

Sources 

1.  W H Blaaw: The Effigy of Sir David Owen in Easebourne Church, SAC 7 (1854) pp22-43
2.  W H Godfrey: Parish Church (and Priory) of St Mary’s, Easebourne, SNQ 13 (May 1952) pp209-12
3.  H Hinkley: Easebourne. Its Church and Priory, Revised 1977 by M C Field
4.  W H St John Hope: Cowdray and Easebourne Priory, London 1919
5.  N Vincent:  A Nuns' Priests' Tale: the Foundation of Easebourne Priory (1216-40), SAC 147 (2009) pp111-23

Plan

Measured plan of church and priory by W H Godfrey in VCH 4 p48