Dedicated to hermit Pietro del Morrone, who was promoted to Pope Celestine V in 1294, this Gothic veteran is most famous for its series of baroque ceiling paintings, executed by Mattia Preti between 1657 and 1673 and depicting episodes from the lives of Celestine V and St Catherine of Alexandria. To the left of the altar, the Cappella Pipino holds 14th-century frescoes of Mary Magdalene, attributed to an anonymous artist known simply as the Maestro di Giovanni Barrile.
Further baroque touches are provided by Cosimo Fanzago, designer of the marble altar, polychromatic balustrade and transept flooring, as well as Massimo Stanzione, whose Madonna Appearing to Celestine V hangs in one of the side chapels on the right. The Conservatorio di Musica San Pietro a Majella di Napoli – one of Italy's finest music schools – occupies the adjoining convent.