The Church of today was built after the granting of a Charter and Borough Status in 1251. The West Front has a recessed porch, with a rare surviving 13th century sculpture. Old Testament figures are carved around the twin doorways. Roundels in the arch have scenes depicting scenes of Christ’s life. The Church has a wide nave with three rows of arches making it a complete square. The earliest is the southern arcade, (Early English period), and about a hundred years later it was widened with an extension to the north and two arcades in the Decorated style. At that time, the roof level was also altered and the clerestory and present roof were added with window traces of the contemporary Decorated style.

The High Altar retains original 14th century tiles on the steps. The Altar, outside the period of Lent, and some other Church festivals, is covered with a leather frontal, a commemoration to local firms trading in the town. The design has symbols of tanning processes of leather, the patron saints of leather-workers - SS. Crispin and Crispinian, and some tools of the leather trade, the four Evangelists, with crown and monogram of the Blessed Virgin.

The Font is from the 13th century, and the Screens and Stalls are 15th century. The Choir has a set of twenty stalls with carved misericord seats.

The Brasses: One of Laurence Seymour on the tomb under a richly decorated arch separating the High Altar from that of the Lady Chapel. A Seymour brass of 1337 is of the last Rector of the parish. The great tithe was later taken away for the foundation of a College at Leicester; this made succeeding parish priests Vicars. It is considered as the finest ecclesiastical brass of its kind. Through the small arch connecting the Lady Chapel with the Chancel there are two brasses (one under the carpet) to commemorate the Chichele family (the Archbishop's parents, Thomas and Agnes), dating 1400, and William (his brother) and Beatrice, his wife, dated 1425. There are nine brasses, including Richard Willeys (a Warden of Chichele's College) and Henry Denton (in the south aisle chapel) a member of the College (died in February 1498) and had been in charge at Chelveston.

Part of the tower and spire fell in 1630 (reconstructed immediately with the same stones). Another restoration was made in the 1850s and the south aisle was rebuilt, with the roof timbers retained. The Rood and its loft were added in 1920.

Generous benefactors have enriched the furnishings: the Comper Hood of 1920, the organ loft by Temple Moore, several stained glass windows, mostly by Kempe Studios, Altar ornaments from the Frank Knight workshops at Wellingborough, and the re-decoration of the fine roof bosses was undertaken in memory of John White, a local shoe manufacturer and benefactor.

The Inner West Porch doors in glass portraying the Annunciation, together with the bell-ringing chamber and balcony were given by the late John White in memory of his wife. The peal of eight bells provide excellent facilities for visiting campanologists from all parts of the country.