He completed his doctorate in theology in 1984 with the thesis Le texte dit lucianique du livre d'Esther.

[3][4] He worked at the Centre d'Études Orientales of the Institut Orientaliste de Louvain of the Université catholique de Louvain and was director and researcher at the Nationaal Fonds voor Wetenschappelijk Onderzoek (NFWO).

[5] He also was a professor at the Catholic University of Louvain-la-Neuve, president of the Belgian Academy for the Study of Ancient Near Eastern Languages (ABELAO[5]) and editor of the online journal BABELAO.

[6] The contribution by Haelewyck in the Septuagint and Jewish pseudepigrapha, addresses the question of the annihilation of the other and reactions to this narrative element in the Greek tradition of the Book of Esther, in the Septuagint, the so-called "Lucianic" text and the Vetus Latina and its Greek model, by comparison with the story of Esther in the masoretic text.

"[9] Kristin De Troyer claim: "these passages are, indeed, very important, albeit in my opinion not for the Old Hebrew but rather for the Old Greek text.