Professor de Saeger graduated in theology from Harvard University; in religious studies from the University of Cambridge; in law from the University of Brussels (VUB) and Hebrew University of Jerusalem; in canon law from the Catholic University of Louvain (KULeuven); and in philosophy of law from the University of Leiden.

A brief overview of his international research:
- at FSCIRE (Fondazione per le scienze religiose Giovanni XXIII) in Bologna with a European fellowship (ReiRes) in June 2019
- at the Sorbonne - EPHE (Ecole Pratique des Hautes Etudes) in Paris with a European fellowship (ReiRes) in April 2019
- at the University of Oxford, where he was a member of Kellogg College and an associate member of the MCR at Exeter College, from 2011 to 2018
- in Harvard University's Dumbarton Oaks Research Library and Collection in Washington DC with a scholarship in May-June 2015 and May-June 2016
- in Gladstone's Library in Wales with the Canon Symonds Memorial Scholarship in February 2015
- in the libraries of the Sorbonne, and the Sainte-Geneviève and Sainte-Barbe libraries in Paris with a Biermans-Lapôtre Foundation scholarship in the autumn and winter of 2011-12
- in the Vatican Apostolic Secret Archives in January 2011

Short-term academic courses:
- European University Institute of Florence: European Law and Human Rights
- The Hague Academy of International Law: International Public Law
- University of Cambridge: English Legal Methods

Professor de Saeger teaches in Belgium at PXL University College in Limburg and in the United Kingdom at the University of Cambridge.
Previously, he taught at various colleges of the University of Oxford (2013-17) and at the University of Brussels (ULB), campus Mons (2015-17).
From time to time, he teaches as a visiting professor or researcher at other universities and seminaries.