Son of Count Dominico Ludovico Pecci and Anna Prosperi Buzzi; older brother of Pope Leo XIII. Studied at the Jesuit College in Viterbo, Italy from 1818 to 1824. Entered the Jesuits in 1824. Studied at the Jesuit College in Rome, Italy from 1824 to 1828. Taught theology at the Pontifical Gregorian University in Rome in 1847. Taught at the theological seminary in Perugia, Italy from 1852 to 1859. Taught at La Sapienza University in Rome in 1860. Helped prepare the documents for Vatican Council I. Created Cardinal–Deacon of San Agata de’ Goti on 12 May 1879. Prefect of the Congregation for Studies on 16 February 1884. Helped lead the Neo-Thomist revival in theological thought. Head of the re-vitalized Vatican Library.
- 8 February 1890 from pneumonia
- buried in the chapel of the Society of Jesus in Campo Verano Cemetery, in Rome, Italy