The seal of Carlow University is designed to represent visually those values and ideals that are held by the Sisters of Mercy who founded the university, and that are expressed in the Mission Statement. Enclosed within the circle, a symbol of eternity, and open to the circle at each of its points is a triangle, symbolizing the Trinity.

Within the triangle is the Pennsylvania Keystone bearing the motto "Ad Superna, non Superba" ("to the Eternal, not the Perishable"). On either side of the triangle is the lion rampant, a detail taken from the coat of arms of Catherine McAuley, founder of the Sisters of Mercy. Wisdom, (the five-pointed star), and Knowledge, (the Roman lamp), have a place above and below the Keystone, while the Irish Cross, (recalling the Irish heritage of the Mercy Sisters), and a circle (symbolizing Eternity) are at either side of the Keystone.