Following his education, and after a short period of training at Leuven, studying Latin under Conrad Goclenius, Masius worked as secretary for the bishop of Constance, Johan Weze († 13 November 1548).
Masius studied Hebrew in Leuven, Arabic in Rome with Guillaume Postel and in 1553 Syriac with Moses of Mardin, a priest of the Patriarchate of Antioch in Syria.
In the same year in Rome he translated two creedal documents from Syriac for Yohannan Sulaqa, the (anti-)patriarch-elect of the Church of the East.
De Paradiso Commentarivs : Scriptvs Ante Annos Prope Septingentos / à Mose Bar-Cepha Syro; ... Adiecta Est Etiam Divi Basilii Caesariensis Episcopi leiturgia siue anaphora ex vetustissimo codice Syrica lingua scripto.
Praetera professiones fidei duæ, altera Mosis Mardeni Iacobitæ ... altera Sulaçe siue Siud Nestoriani ... Omnia ex Syrica lingua nuper tralata per Andream Masivm ... Antverpiæ, Ex Officina Christophori Plantini, 1569.In 1571 Masius published his Grammatica linguae syricae as well as the dictionary Syrorum Peculium.