(20 Feb. 1878–20 July 1903)
Sixth child of seven in a family of the lesser nobility, Gioacchino Vincenzo Pecci was born at Carpineto, in the hills south of Rome, on 2 Mar. 1810. A brilliant boy with a flair for Latin which he retained through life, he studied at Viterbo (1818–24), the Roman College (1824–32), and the Academy of Noble Ecclesiastics (1832–7). Ordained in 1837, he immediately joined the papal service and was made governor, first, of Benevento (1838–41), and then of Perugia (1841–3), proving in both a firm and capable administrator. Gregory XVI then sent him as nuncio to Belgium (1843–6), first appointing him titular archbishop of Damietta. This, with short visits to Cologne, London, and Paris, was his first contact with industrialized, parliamentary Europe, but his ill-judged support of the episcopate against the government in an educational controversy led King Leopold I (1831–65) to request his recall. He was then bishop of Perugia 1846–78, being named cardinal priest of S. Crisogono in 1853 but kept from Rome and curial responsibilities because he was suspect to Cardinal Antonelli, Pius IX's secretary of state. As bishop he protested against the annexation of Perugia by Sardinia in 1860 and the secularizing legislation that followed. He also modernized the curriculum of his seminary, promoted a revival of Thomism and founded (1859) the Academy of St Thomas Aquinas, and began (as his pastoral letters of 1874–7 reveal) to argue for a rapprochement between Catholicism and contemporary culture. After Antonelli's death Pius IX recalled him (1877) to Rome as camerlengo, i.e. the official who administers the church in a vacancy. At the conclave of Feb. 1878, the first since the loss by the holy see of its temporal power, he was elected as an intelligent moderate at the third ballot. He had to be crowned in the seclusion of the Sistine Chapel because the government feared demonstrations in his favour if he blessed the Roman crowd from the loggia of St Peter's. Almost 68, fragile in health, he seemed, and was possibly elected as, a stopgap appointment, but ruled the church with masterly flair for over 25 years.
Leo's main achievement was his attempt, within the framework of traditional teaching, to bring the church to terms with the modern age. At the same time he made no sharp break with Pius IX, whose policies he continued in several fields. For example, his attacks on socialism, communism, and nihilism in Quod apostolici muneris (28 Dec. 1878), or on Freemasonry in Humanum genus (20 Apr. 1884), as his treatment of marriage in Arcanum illud (10 Feb. 1880), could have come from Pius' pen. Far from halting centralization, as progressives hoped, he increased it by intervening with national episcopates, strengthening the position of nuncios, and concentrating orders and congregations in Rome. But his distinctive contribution was the opening up of dialogue between the church and society in a striking series of pronouncements. In the intellectual field he directed Catholics (Aeterni Patris: 4 Aug. 1879) to the philosophy of St Thomas Aquinas (d. 1274), and founded an academy at Rome to study it and to produce a definitive edition of Thomas's texts, a work still in progress and known, in the pope's honour as ‘the Leonine edition’. He also fostered the study of astronomy and natural sciences at the Vatican, called on Catholic historians to write objectively, and opened (18 Aug. 1883) the Vatican archives to scholars regardless of creed. To meet the challenge of new critical methods he laid down guidelines for biblical research in Providentissimus Deus (18 Nov. 1893). He devoted several encyclicals to the sociopolitical order, defining, e.g., the spheres of temporal and spiritual power in Immortale Dei (1 Nov. 1885), giving a grudging recognition to democracy in Diuturnum illud (29 June 1881), and arguing in Libertas praestantissimum (20 June 1888) for the church as the custodian of liberty as properly understood. In these (especially Immortale Dei) he was at pains to affirm the legitimacy of any form of government, even republicanism, provided it ensured the general welfare. His most famous manifesto, Rerum novarum (15 May 1891), upheld private property, but also the just wage, workers' rights, and trade unions; though condemning socialism, its advocacy of social justice earned him the title of ‘the workers' pope’.