The Council of Trent having recommended a revision of the Sacred Scriptures, Agelli was one of the learned men selected by Pius V to whom this important work was confided.
Their attention was first directed to the Septuagint version, on which Agelli was principally employed, and for which he collated a vast number of Hebrew and Greek manuscripts.
He was also one of the six persons, called scolastici, who presided over the Vatican press, and examined the works to be printed there, by comparing them with good manuscripts.
Clement VIII held him in such high esteem, that he entrusted to him the education of his grand nephew, Ippolito Aldobrandini, made him consultore of the Congregation of the Index, and in the year 1593 bishop of Acerno, in the Campagna Felice.
In addition to his editorial labours mentioned above, he wrote the following works, which are described by Ughelli as most accurate, copious, and valuable: In addition to the above, the following works are preserved in manuscript in the Quirinal Library of the Regular Clerks: He likewise assisted Mario Altieri in the correction of the Gallican Psalter, and by order of Clement VIII made a strict criticism of the Talmud.