The frieze of the entablature is highly enriched, and in the tympanum of the pediment are the royal arms. On the acroteria of the pediment are three statues by John Smyth: Mercury on the right, with his Caduceus and purse; on the left Fidelity, with her finger on her lip, and a key in her hand; and in the centre Hibernia, resting on her spear, and holding a harp. The entablature, with the exception of the architrave, is continued along the rest of the front; the frieze, however, is not decorated over the portico.
A handsome balustrade surmounts the cornice of the building, which is 15,2 metres (50 ft) from the ground. With the exception of the portico, which is of Portland stone, the whole is of mountain granite.
The interior contains a large open postal hall with an elevated mezzanine level over the counters. An elaborate coffered ceiling with grecian designs floats serenly overhead.
The GPO has a special place in Irish and Dublin history being the focal point of the Easter Rising of 1916, it served as the headquarters of the uprising's leaders. The assault by the British forces extensively damaged the building and it was not repaired until the Irish Free State government took up the task some years later. The original columns outside are still pocked with bullet-marks. As the Proclamation of the Irish Independence was read within the GPO, an original copy of the Proclamation of the Irish Republic is on permanent display in the GPO philatelic office. The building has remained a symbol of Irish nationalism and Irish national history. In commemoration of the failed Rising, a statue depicting the death of the mythical hero Cùchulainn is housed in the front of the building.