Sebastian, was born about the year 1515. Chatillon, Dauphiny, and Savoy, are mentioned by different authors as the place of his birth. He early gained the esteem of Calvin, who lodged him in his own house at Strasburg, and procured him a regent's place in the college of Geneva. In this office Castello continued till 1544, when he was forced to quit it on account of his peculiar opinions concerning Solomon's Song and Christ's descent into hell. He retired to Basle, where he was made Greek professor; and died in great poverty in 1564. He incurred the displeasure of Calvin and Beza by differing from them in his doctrines concerning predestination and the punishment of heretics. His works are numerous. In 1545 he printed at Basle four books of dialogues, containing the principal histories of the Bible, in elegant Latin; but his principal work is a Latin and French translation of the Scripture.

The Latin translation he began at Geneva in 1542, and finished at Basle in 1550. It was published there in 1551, and dedicated to Edward VI. king of England. The French translation was dedicated to Henry II. of France, and printed at Basle in 1555. The translation is greatly disfigured by the affectation of using only classical terms. Besides these Castello wrote a Latin translation of the Sibylline verses, a Greek poem on John the Baptist, a translation of several treatises of Bernardo Ochino, and notes on the Epistle to the Romans.