They are the surviving fabric of the medieval town wall itself, folded into the churchyard's edge as if the town simply grew around the building and eventually surrendered that corner of its defences to the dead. The church occupying the north-west angle of the old town is known formally as the parish church of the Assumption of the Blessed Virgin Mary, though for centuries it went by the more familiar name 'Our Ladye of Clonmell'.

The foundation dates from the 13th century, attributed to William de Burgh or his son Richard, and the earliest written evidence for it comes from an unexpected source: a letter by Abbot Stephen of Lexington, who preached here in August 1228 during a visit to the nearby Abbey of Inishlounaght. By the late 14th century the building had fallen into serious disrepair after a series of attacks on the town. James, Earl of Ormond, declared that parishioners could no longer attend divine service there. What rose in its place was a fortified church, built in the late 14th or early 15th century with crenellated battlements along its side-walls and gable ends, giving it the silhouette of a minor castle rather than a place of worship. An excavation in 1996 uncovered a sarcophagus from this same period protruding from the base of the tower, which itself had been built directly onto the chancel without foundations. A sketch made by Daniel Grose in the late 18th century captures this medieval structure before it was substantially altered, showing the White Mortuary Chapel of 1622 to 1623 projecting southward from the nave, a wooden fleche and belfry atop the octagonal tower, and dormer windows running along the aisles. The renovations of 1805 were considerable: the chancel was shortened by nearly nine metres, the White Memorial Chapel was demolished, and its altar-tomb, armorial stone, and architectural fragments were relocated to the church at Patrickswell, roughly three kilometres to the west. The internal galleries were removed, though the bells, dated 1697, were left in place. A rebuild in 1857 went further still, and most of what stands today is 19th-century construction, with the lower half of the octagonal belfry and the 15th-century east and west windows among the few genuinely medieval survivors.

The graveslabs inside the porch and nave reward close attention. Several date from the 17th century, including one for John Striche and his wife Margaret Smith from 1625, and another for John White from 1643. The earliest of all, a slab of 13th or 14th-century date, was uncovered only in the 1990s at the west end of the nave, a reminder that the ground here holds considerably more than the current building suggests.