He was converted about 1540 to the Catholic faith through Cardinal Pole but embraced Protestantism in the following year, before going to Strasbourg to teach Hebrew.
Owing to the Schmalkaldic War in Germany, he was compelled to seek asylum in England, where he resided at Lambeth Palace with Archbishop Cranmer in 1547.
Harris Fletcher remarks that there were two quite different versions of Tremellius available in the late 1500s: The Junius-Tremellius Bible first appeared from 1575-79, and subsequently in two different major forms.
One of these in 1585 was printed as a tall folio with copious marginal notes, which were for the greater part written by Tremellius.
The other form in which this Bible appeared was printed, usually in quarto, without notes, with the Apochrypha, and after 1585 with only Beza's translation of the New Testament.