The episcopal complex, which comprises the basilica itself, a sacristy, a baptistery and the bell tower of the nearby archbishop's palace, is an excellent example of early Byzantine architecture in the Mediterranean region.

The Euphrasian basilica has for the most part retained its original shape, but accidents, fires and earthquakes have altered a few details.

The floor mosaic from its oratory, originally part of a large Roman house, is still preserved in the church garden.

Following the earthquake of 1440 the southern wall of the central nave of the basilica was restored, so that in place of the windows which were destroyed, other were built in the Gothic style.

[1] The basilica is part of a complex composed of: The two aisles are separated from the nave by 18 elegant Greek marble colonnades with richly sculpted Byzantine and Romanesque capitals, decorated with depictions of animals.

A novelty of the Euphrasian basilica is that rather than being enclosed by a straight wall, as all sacred buildings were up to that time, it makes use of the breadth and length of the apse of the central nave, built in the shape of a polygon from the outside, whilst the two aisles end in smaller semicircular apses, hollowed into the wall.

[2] The mosaics in the triumphal arch over the apse represent Christ; holding an opened book with the Latin text "Ego sum lux vera" ("I am the true light") with the Apostles, each with their attribute, The arch below contains mosaic medallions with the Lamb of God and portraits of twelve female martyrs.

The vault over the apse is decorated with mosaics with Mary and Child, sitting on the Heavenly throne, under a wreath held by a hand - symbol of God the Father.

The front wall of the apse is framed with a narrow decorated band filled with praise of Euphrasius and his works.

The apsis is dominated by the marble ciborium, modelled after the one in St. Mark's in Venice,[4] it was built in 1277 on the orders of Otto, Bishop of Poreč.

In the 15th century Bishop Johann Porečanin ordered in Italy a Renaissance relief for the antependium of the altar, made of gilded silver.