During this time, he also worked as a writer and radio talent for the Chesteron Evidence Guild, more specifically, the "Common Weal Hour", for which he created the character of Teban, the calesa driver, at the height of the controversy over the 1940 divorce bill.
The program evolved into "Kuwentong Kutsero", consisting of satirical tales dealing mostly with life in Manila.
Early in 1946, he left for the United States to pursue further studies in theology at Woodstock College, Maryland, where he was ordained a priest on March 24, 1946, by American Bishop John F. McNamara.
Back in the Philippines, he served anew with the faculty of the Ateneo de Manila in 1953, later becoming its first Filipino college dean while teaching history at the same time.
In 1965, he was presented the Republic Heritage Award by the then Philippine President Diosdado Macapagal for his historical writings.
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.
A few years before his death, De la Costa attended the General Congregation of Jesuits from all over the world in Rome.
In 2016, the Bangko Sentral ng Pilipinas released a limited edition one-peso commemorative coin in honor of de la Costa's 100th birth anniversary.