It was founded at the end of the 11th century as a large cruciform church which, due to its original scale, has been described as a collegiate church—a reflection of the port of Shoreham's importance at the time.

[1] Claims that it was founded near the place (Cymenshore) where Ælle of Sussex—the first King of the South Saxons—came ashore in 477 have been disproved, but it had become a successful village by the time of the Domesday survey in 1086, supporting a population of 76.

[1] In the decade after this, William de Braose, 1st Lord of Bramber or his son Philip founded a new settlement to the south, on the estuary where the Adur flowed into the English Channel.

[1][2] Its harbour quickly became prosperous and successful: it overcame the competition from contemporary inland Sussex ports such as Arundel and Steyning, and gained royal patronage when King John's fleet was stationed there in the early 13th century.

[4] The present building—a large edifice itself, bigger than the small-scale buildings of the town—[6][7] is merely the surviving east section of a much more substantial church, which would have been cruciform when built by the de Braoses.

[4][6][7][8] By 1500, however, no male heirs were left and the de Braoses' estates and holdings were broken up; and erosion and changing tidal activity made the port dangerous to sail into and had washed away parts of the grid-pattern town.

As originally built, the church had a tower and a nave, beyond which was a chancel with an apse and east-facing rounded chapels at the east end;[7] the outline of these can still be discerned.

[7] Its influence was also at its highest, as it had gained administrative independence from St Nicolas' Church, the de Braoses still wielded considerable power and the Port of Shoreham was thriving:[9] King John stationed ships there and established a prison in 1221.

[2][4] Minor structural alterations took place, such as the construction of a porch, a rood screen and an accompanying altar, but the fabric of the church gradually disintegrated.

[4][9] During the 19th century, some work was undertaken in the interior, including Arthur Loader's replacement of some original Perpendicular Gothic-style aisle windows with Norman-style equivalents in 1876.

[4][9] A less durable stone was used for interior structures; some of these (for example a door at the west end) were exposed by the collapse of the original nave, and have experienced severe weathering.

[1] It covers the ancient grid-pattern town centre and High Street area, as well as a small section of land on the west side of the River Adur.