Fr. de la Costa received a Smith-Mundt-Fuldright scholarship in 1960. In 1962, he became a research associate of the London School of Oriental and African Studies. During this period, he received honorary doctorates from the University of Santo Tomás, Tokyo's Sophia University, and Dumaguete's Silliman University. On December 8, 1964, he assumed office as provincial superior of the Philippine province of the Society of Jesus. His appointment ended the long line of Spanish and American Jesuits who were appointed to the said post in the Philippines. De la Costa was the author of a number of books, particularly on Philippine culture and history, which revealed his nationalistic bent, among which are:   He also contributed numerous articles on these subjects to various local and foreign scholarly publications, such as "Philippine Social Sciences and Humanities Review", "Bulletin of the Philippine Historical Association", "Hispanic American Historical Review", "Comment", "Science Review", "Theological Studies", and . The Catholic Encyclopedia carries his article on the Philippines. In 1965, he was presented the Republic Heritage Award by the then Philippine President Diosdado Macapagal for his historical writings. In 1971 he became General Assistant to the Superior General of the Society of Jesus, Pedro Arrupe, in Rome. Fr. de le Costa was one of the founding members of the Philippine Academy of Science and Humanities, as well as the International Association of Historians of Asia. He was also a member of the National Research Council of the Philippines, Philippine Bibliographical Society, Philippine Historical Association and the National Historical Society of the National Historical Commission. A few years before his death, De la Costa attended the General Congregation of Jesuits from all over the world in Rome. In need of a composition on "The Jesuits Today", the delegates entrusted him the preparation. He worked on it by himself for three days. When he was finished, he returned to the congregation and read his draft. His composition was accepted exactly as he had written it. De la Costa died of cancer on March 20, 1977 at the age of 60. He was buried in the Jesuit Novitiate Compound in Novaliches, Quezon City. For his achievements in the Jesuit Philippine Province and the Jesuit congregation in general, the Loyola School of Theology of the Ateneo de Manila University was inaugurated while the Horacio de la Costa Hall in the same university was named, both in his honor. A street in Salcedo Village in Makati's central business district, where the Ateneo de Manila's Salcedo Campus (which is home to the university's Graduate School of Business and the Center for Continuing Education) is located has been named in his honor as well.