[1] Oakley's graduate studies were interrupted by the need to return to England to serve for two years (followed by reserve duty) in the British Army, where he rose to the rank of lieutenant in the Royal Corps of Signals and was attached to the Commonwealth Communications Army Network (COMCAN).
Oakley has held visiting research appointments at the Institute for Advanced Study in Princeton, New Jersey, the National Humanities Center in North Carolina, and the Woodrow Wilson International Center for Scholars in Washington, D.C. During the academic year 1999-2000, he held the Sir Isaiah Berlin Visiting Professorship in the History of Ideas at Oxford University.
Oakley has written extensively on topics pertaining to medieval and early modern intellectual and religious history and to American higher education, and is the co-editor of three volumes as well as the author of fifteen books.
Prominent among the latter are his Omnipotence, Covenant and Order: An Excursion in the History of Ideas from Abelard to Leibniz, (1984), Community of Learning: The American College and the Liberal Arts Tradition (1992), and The Conciliarist Tradition: Constitutionalism in the Catholic Church 1300-1870 (2003), which was awarded the Roland H. Bainton Book Prize in 2004.
[2] For ten years, Oakley worked on a trilogy with the overall title of The Emergence of Western Political Thought in the Latin Middle Ages, published by Yale University Press between 2010 and 2015, and for which he received the 2016 Haskins Medal from the Medieval Academy of America.