Gillespie subsequently returned to Rome to study for his doctorate. While there he led the procession of cardinal electorss into the conclave which chose Jorge Mario Bergoglio to succeed Pope Benedict XVI (and with whom Gillespie also worked closely). Gillespie then served as Papal Master of Ceremonies for the new pope. He assisted Francis during his first Easter Sunday Mass at St. Peter's Basilica on 31 March 2013. Photographs included in national and international media showed Gillespie standing to the right of Pope Francis. Gillespie had earlier led Holy Thursday Mass at the Pontifical Irish College in Rome. Gillespie was part of the Papal Delegation accompanying Pope Francis during his visit to the Philippines in January 2015 and was also present when Pope Francis declared Mother Teresa a saint in St. Peter's Square in September 2016. He joined Members of the Colloquium of Anglican and Roman Catholic Canon Lawyers at their May 2017 reunion in Rome, following their establishment by the Pontifical University of Saint Thomas Aquinas ("Angelicum"), the Centre for Law and Religion at Cardiff University and Duquesne University School of Law. He was also involved in the World Meeting of Families 2018, which coincided with Pope Francis's visit to Ireland. During the COVID-19 pandemic, Gillespie agreed to celebrate weekday morning Mass for the nation on RTÉ Television.