The architectural history of the building is highly complex and much remains unsolved. The Romanesque parts of the church consist of the S chancel wall, the S transept, which is dated to c. 1170 or slightly later, and the N transept, which is slightly later in date than the S transept. The S wall of the S transept was remodelled in the 19thc. The barrel-vaulted chapel of St Nicholas is situated to the E of the N transept. The pointed W tower arch is late 12thc, decorated with string course and sculpted capitals. Round-headed nave arcades. The S nave arcade dates to c. 1200, the N nave arcade is 13thc. N and S transept doorways decorated with sculpture, both late 12thc. Plain W doorway, somewhat earlier than S and N transept doorways. S porch c. 1200 decorated with sculpture both on exterior and interior, leading to S doorway also decorated with sculpture. The church is constructed of local red sandstone.

Anglo-Saxon foundations were discovered during excavations in 1864. This church was rebuilt in c. 1150. In the 12thc and 13thc St Mary's was a collegiate church, later raised to the status of a Royal Free Chapel. Extensive work was carried out between c. 1190 and 1220 and again between 1460 and 1480. The chapels-of-ease of St Mary were Albrighton, Clive and Astley. St. Mary's College was dissolved in 1548, but St Mary's kept its status as a Royal Free Chapel until 1846. The church was extensively restored by S. Pountney Smith in 1867-70.

The decoration on the third pier of the S nave arcade (second order, S face) and of the W impost pier is reminiscent of the carving on the capitals of the chancel arch at Wroxeter.

Sedilia with authentic Romanesque ornament are extremely rare, so interpreting the fragment in the S wall of the chancel is significant. Although the church's collegiate status would fit will with the presence of early sedilia (re: St Mary de Castro, Leicester), the fragment is clearly reset so not good evidence of there being sedilia in the Romanesque church.