The Chapel of Our Lady of the Pilar is an independent space within the Basilica, integrated in the set of the naves but with its own scale and design. It was built between 1750 and 1765 following the project of Ventura Rodriguez, who devised an authentic architectural jewel box to enhance the image of the Virgin. The work was done in classicist baroque style, combining cut domes, curved entablatures, breaks of glory, and abundant sculptures and marble medallions.

Although Ventura Rodríguez designed the chapel, he only visited El Pilar on two occasions, so he delegated the direction of the works to José Ramírez de Arellano, who was also responsible for the sculptural groups in the interior. The chapel was conceived as a baldachin inside the church and is located under the second bay of the central nave.

Its plan is in the form of a Greek cross with rounded tops and is covered by an elliptical dome resting on an undulating entablature with four lobes. The dome is perforated with openings that allow the entrance of natural light, creating a luminous effect on the interior. The entire ensemble is adorned with sculptures in relief and free-standing, following a program that seeks to highlight the Virgin's niche, located slightly off to the right with respect to the central axis. The design combines influences from the architecture of Bernini and Borromini, the Byzantine style, Rococo and the first elements of neoclassicism.