The architectural configuration of the church of Cap d'Aran follows the principles of Romanesque style architecture, having a three-nave basilical ground plan with a barrel vault headed by three apses. The most recent restoration work carried out on the church revealed the different building stages involved in its evolution. In fact, the roof appears to have collapsed at least twice. Another detail which brings this succession of structural collapses to light is the continual reuse of building materials, which is particularly noticeable in certain specific areas such as the windows, facade and apse.

The church of Santa Maria de Cap d'Aran de Tredòs features two unusual characteristics in contrast to the rest of the ecclesiastic heritage of the Aran Valley: the presence of a crypt below the altar and the siting of the belfry, which is removed from the main temple building. The crypt comprises two areas, one rectangular and the other semicircular, separated by a semicircular arch. As far as the belfry is concerned, although it contains the beginning of what was possibly the original Romanesque belfry, the rest of the body of the building is composed of additions from later periods.

Finally, it should be mentioned that the church of Cap d'Aran originally had Romanesque wall paintings attributed to the circle of the Master of Pedret in the 11th and 12th centuries. These paintings were forcibly removed and taken out of the Aran Valley; they can now be seen at The Cloisters Museum in New York.