The Latin inscription carved above the recumbent figure of Archbishop Miler MacGrath includes the lines: "Here where I'm plac'd I'm not; and thus the Case is, I'm not in both, yet am in both the Places." It is a deliberately paradoxical epitaph, composed by the archbishop himself, and it suits a man whose religious loyalties were, by almost any measure, deeply ambiguous.

MacGrath's monument, dated 1621, occupies a moulded round-headed recess of limestone, the imposts continuing as a string-course to the rear. The effigy, measuring roughly 2.1 metres in length, shows him in the long robe and mitre of an archbishop, his feet resting on a dog with outstretched front quarters, a conventional symbol in medieval and early modern funerary sculpture. An orb decorated with a clover-leaf cross flanks one side of his head, and two winged cherubs appear at the upper corners of the tomb. Decorative panels fill the side walls of the recess, one showing the crucified Christ, the other an episcopal mitre bearing MacGrath's heraldic arms. Those arms are elaborately quartered on a plaque above the effigy: leopards passant regardant, a hand holding a battle-axe, a hand holding a cross patee, and a stag salient, with a crest of a male head rising from a knight's helmet with mantling terminating in tassels. The sculptor signed his work in a pentameter carved along the base of the slab: Patricius Kerin fecerat illud opus, "Patrick Kerin made this work." MacGrath's verse inscription addresses any passer-by directly, invoking St Patrick's tenure as bishop at Down and noting, with a certain wry self-awareness, that he himself had served England for fifty years amid its religious and political upheavals. The closing lines, "He that judgeth me is the Lord" and "Let him who stands, take care lest he fall," read less like conventional piety than like a man who knew he had given his critics plenty of material.

A photograph taken in 1901 recorded a fragment of a carved graveslab with a Latin border inscription at the base of the monument, but that fragment has since disappeared. There is also evidence that the front of the tomb may originally have been finished in stucco work framing the heraldic plaque, which would have given the whole composition a rather different, more colourful appearance than what survives today.