Following World War II, she undertook further study in philology and oriental history at the Catholic University of Leuven, where she completed her doctoral thesis in 1954.
[2] Her research focussed on South Arabia (Yemen), especially ancient Sheba and Qataban, and the Semitic languages of the Arabian Peninsula.
She continued to argue for this chronology in subsequent work, making use of palaeographic evidence for changing letter-forms in inscriptions, such as those of Al-Masajid.
[2] From 1957 to 1985, she worked at the Centre national de la recherche scientifique (CNRS), eventually rising to the position of Director of Research.
[2] After leaving the CNRS in 1985, Pirenne spent two years in Addis Abeba, working on the chronology of the kings of Aksum and helping to support Ethiopian orphans.