St Mary's possesses an eccentric Baroque porch, designed by Nicholas Stone, facing High Street, and a spire which is claimed by some church historians to be one of the most beautiful in England.

[4] Early provosts of the college were inducted into their stall in the church, and until 1642 fellows were required to attend services on Sundays and holy days.

[2] St Mary's was the site of the 1555 trial of the Oxford Martyrs, when the bishops Latimer and Ridley and Archbishop Cranmer were tried for heresy.

The martyrs were imprisoned at the former Bocardo Prison near St Michael at the Northgate in Cornmarket Street and subsequently burnt at the stake just outside the city walls to the north.

Cranmer stood on a stage, the corner of which was supported by a small shelf cut from the pillar opposite the pulpit; withdrawing his recantations of his Reformed beliefs, he swore that when he was burnt, the hand which had signed them would be the first to burn.

This project was cut short by the fall of Laud and the outbreak of the English Civil War, but after the Restoration, it was revived and carried through by John Fell, Dean of Christ Church, who commissioned Christopher Wren to erect what became the Sheldonian Theatre.

From the present pulpit John Keble preached the assize sermon of 14 July 1833, which is traditionally considered to have started the Oxford Movement, an attempt to revive catholic spirituality in the church and university.

It is highly ornate, with spiral columns supporting a curly pediment framing a shell niche with a statue of the Virgin and Child, underneath a Gothic fan vault.

The style was too close to Roman baroque for the puritans of the day and the porch itself was used as evidence in Laud's execution trial, citing its "scandalous statue" to which one witness saw "one bow and another pray".

The north wall of de Brome's chapel and the congregation house were remodelled in the Perpendicular style around 1510, and new windows were added to match the others in the church.

The interior space has six-bay arcades with shafted piers, between the clerestory windows, are canopied niches with archangels holding shields.

The roof has traceried spandrels, the chancel has transomed windows, and the sedilia is decorated with cusped arches and a frieze of vine leaves.

Monuments include a slab with indents of a brass cross and the Virgin and Child, thought to commemorate Adam de Brome, from 1332, though the tomb chest is modern.

Much altered over the years, the last remains of this original organ (besides some fragments of ornamental casework and, possibly, part of one stop) were destroyed by a fire shortly after the Second World War.

It still lacks certain decorative carvings from the original design by Bernhardt Edskes, most notably the large scrolls beneath the pedal towers on the four corners.