On the exterior, the atrium that surrounds a large part of the church stands out, except for the main façade called the Glory façade, giving it a U-shape of 115 by 82 meters. This innovative idea of Gaudí differs from the traditional layout of the atriums in early Christian basilicas and medieval monasteries, which are usually located at the side of the church. Gaudí chose this layout to isolate the church from outside influences, both acoustic and climatic, and to facilitate processions. The atrium, like the overall design, rises four meters above the ground and measures 240 meters in total.

In the windows of the exterior walls, Gaudí devised three distinct styles to transition from the original neo-Gothic to the new naturalistic structure that characterizes his later works. The first level, under the cantoria, presents a neo-Gothic style; the second level, above the cantories, has an elliptical hyperboloid shape surrounded by four circular shapes in a frieze with elongated openings; the third level, corresponding to the central nave, also exhibits an elliptical hyperboloid shape surrounded by two hyperboloids of revolution, also above four elongated openings, with the inscription "Gloriam" in the center.

Between the windows of the side naves, there are Solomonic columns with inscriptions such as "aurum, thus, myrrham" (gold, incense and myrrh in Latin) and "oració, sacrifici, almoina" (prayer, sacrifice and alms in Catalan), topped with the Greek letters "α" (alpha) and "ω" (omega). On the exterior walls also alternate other inscriptions such as "Jesus, Maria, Joseph", "Sursum corda", "Gratia plena" and "Ora pro nobis".