Gallars was of noble birth, and "possessed legal training, rich exposure to the humanities, and polished Latin.
"[1] He first appears as author of a Defensio of William Farel, published at Geneva in 1545, followed (1545–1549) by translations into French of three tracts by John Calvin.
Scott Manetsch notes that Gallars' appointment "signaled an important new stage in Calvin's recruitment efforts.
Calvin held him in high esteem, employing him as amanuensis, and as editor as well as translator of several of his exegetical and polemical works.
His main work was his edition of Irenaeus (1570) with prefatory letter to Grindal, then bishop of London, and giving, for the first time, some fragments of the Greek text.