The priory church of St Mary and St Martin is one of the oldest examples of Norman architecture in the country. It was part of a Benedictine monastery founded in 1088.
The original foundation commenced, AD 1088, with a Norman apse, and proceeded consecutively with the choir, transept, central tower, nave, and aisles. The existing portions of the north aisle with its vault; of the nave with its round arches, massive piers, cushion capitals, triforium, clerestory, and corbel table; and of the south wall of the transept; all harmonise with this date.
The first change which the church, thus constituted, underwent was the substitution of an excellent early-English groined vault, with moulded ribs and elaborate bosses over the nave, for the original roof of wood. This took place about the year 1250. In the centre of the roof of each bay two ribs intersect each other at a boss, and the vault of the bay is completed by two transverse ribs. The work is light and elegant, and bears a strong resemblance to the vaulting of the nave of Durham Cathedral, and south choir aisle of that of Lincoln. The next change was the expansion of the south narrow Norman aisle for the purpose of forming a parish church.
The earliest vicar of Blyth, the date of whose institution is on record was William de Flecham, AD 1256. He was vicar for nearly forty years, and appears to have had a long dispute with the convent respecting the vicarial tithes, which was settled by a deed of endowment, bearing date 1287.
Not long after this the alteration in the south aisle was made. It was widened to the extent of the termination of the south wing of the transept; the old round-headed opening between the transept and aisle was replaced by two more open and pointed arches, now blocked up; and the windows inserted in the south wall, which exist at this day, and which, with the two arches just named and other features, harmonise with the date above assigned. The internal apertures of these windows are splayed from the sill to the springing of the arches; the upper portions are arched over the lights of the window with arches dying into the splayed jamb, with label mouldings and carved terminations. Henceforth the convent and the parish possessed each their own chancels, which in process of time were defined by two separate rood-lofts in a line with each other, crossing the nave and south aisle. The latter of these screens remains, and the painted figures were brought to light in 1842 from the boards and matting of pews, behind which they were concealed, may now be seen with sufficient distinctness, though with a few marks of puritanical violence; with the exception of that of St. Ursula, which was found in such a state of decay as to justify its removal to a place of safe preservation. Other figures on the panels of the parish rood-screen have been cut away to make a road to the reading-desk and pulpit. The rood-loft of the convent has fared worse. With the exception of a fragment at the corner of the private gallery of Blyth Hall and the lower panels, it has been destroyed; and these panels were daubed over with paint, so as completely to obliterate the figures, except at the very base.
The next change which the church underwent was the construction of the present tower, which possesses great beauty, and is a striking feature both of the church itself and of the surrounding country. From an examination of the nave, both within and without, it is clear that a portion of it was taken down to make room for the tower, which at its two western angles, where it is not engaged in the wall of the nave, is flanked with buttresses of seven stages at right angles with the sides, is lighted with double-transomed belfry windows, and crowned with a remarkably light and elegant parapet, whilst its western door is decorated with crocketed canopy and buttresses pierced with panels, above which are three niches of good character, one elevated above the other two, containing in ancient times, we may presume, figures of our Lord, the blessed Virgin, and St. John the Evangelist, long since removed. The tower was built about the middle of the fifteenth century, and no work of any importance was done after it apart from the usual Victorian 'improvements'.