Due to the national mobilization during the War, Georgetown's campus became a testing ground for the Army Specialized Training Center. During O'Leary's presidency, the Graduate School of Arts and Sciences was re-established as an independent school within the university. This was part of O'Leary's aim to have Georgetown meet the Association of American Universities' standard for graduate education. He also increased the number of graduate faculty and students and made major significant improvements to the library's holdings. By 1937, the school began awarding doctoral degrees once again in some departments. In the law school, O'Leary decided to condense the two leadership positions of dean and regent (the latter of which was always a Jesuit) into a single position, due to the resignation of the previous dean. Toward the end of his presidency, O'Leary's health began to deteriorate. He underwent surgery to remove kidney stones in 1937. Soon after the operation, he again became seriously ill and nearly died. As a result, he went to New England and Jamaica for several months to recuperate, returning to the university in October 1937. With his illness progressing, in December 1942, the Jesuit authorities took the unusual step of replacing the president of the university during wartime, naming Lawrence C. Gorman as his successor. In 1947, O'Leary replaced James A. McCarl as the pastor of Holy Trinity Church in Georgetown. Obtaining permission from the Metropolitan Police Department, he began the practice of students at the Holy Trinity School using N Street as their playground for recess. He remained pastor until 1953, when he was succeeded by Emory Ross. His final assignment was as pastor of St. Andrew-on-Hudson, which he held until his death. O'Leary died on February 8, 1962, at Georgetown University Hospital. The requiem mass was held at St. Aloysius Church in Washington, D.C.