- Annibale Francesco Clemente Melchior Girolamo Nicola della Genga
Born to the Italian nobility, and sixth of ten children born to Count Flavio della Genga and Countess Maria Luisa Periberti di Fabriano. Studied at the Collegio Campana in Osimo, Italy beginning in 1773, the Collegio Piceno in Rome, Italy in 1778, the Pontifical Academy of Ecclesiastical Nobles in Rome in 1783. Sub-deacon in 1782; deacon in 1783. Ordained on 14 June 1783.
Privy chamberlain to the Pope. Private secretary of Pope Pius VI from 1783 to 1784. Papal ambassador to Switzerland in 1784. Guest professor at the Pontifical Academy of Ecclesiastical Nobles. Prefect of the Vatican Seminary. Preached the funeral oration of Emperor Joseph II in 1790. Canon of Saint Peter’s Basilica in 1792. Abbot commendatario for life of the Abbey of Monticelli. Titular archbishop of Tiro on 21 February 1794. Papal nuncio in Cologne, Germany from 14 March 1794 until 1800 when he retired to Monticelli Abbey where he planned to spend the rest of his days as a prayerful hermit.
He was recalled from retirement on 23 September 1805 to serve as papal nuncio to the Diet of Ratisbon. With Cardinal Giovanni Battista Caprara, he was a negiator between the Vatican and Napoleon Bonaparte in 1808, but the mission failed. Papal envoy to King Louis XVIII on 22 July 1814. He then retired to Monticelli for another two years.
Created cardinal–priest on 8 March 1816. Archbishop of Senigallia on 8 March 1816, but his health failed, and he resigned on 10 September 1816. Prefect of the Sacred Congregation of Ecclesiastical Immunity on 9 May 1820. Vicar general for the city of Rome on 12 May 1820. Archpriest for the Liberian basilica on 10 February 1821. Reluctant 252nd pope in 1823; he fearing that his health would not permit him to work. He took the name Leo XII, and held the throne for over five years.
Re-instated papal civil authority in the Papal States. Opposed groups that distributed unauthorized Bible editions and translations, and warned against private interpretation. Opposed indifferentism which advocates the equality of all religions. Opposed secret societies, especially the Italian Carbonari. Tried to strictly rule the city of Rome, which caused great resentment. Revived the practice of Jubilees. Approved the Oblates of Mary Immaculate. Named Saint Peter Damian a Doctor of the Church. Saint Vincent Strambi served as one of his advisors. Created 25 cardinals in eight consistories.
- 22 August 1760 at Castello della Genga, Diocese of Fabriano, Papal States (in modern Italy) as Annibale Francesco Clemente Melchior Girolamo Nicola della Genga
- 10 February 1829 in Rome, Italy of natural causes
- interred in Saint Peter’s Basilica
- re-interred before the altar of Saint Leo the Great in the grotto of Saint Peter’s Basilica on 5 December 1830
- Pope Leo XII – Charitate Christi – Extending Jubilee to the Entire Church, 25 December 1825
- Pope Leo XII – Quo Graviora – Condemning Secret Societies, 13 March 1826
- Pope Leo XII – Quod Hoc Ineunte – Proclaiming a Universal Jubilee, 24 May 1824
- Ubi Primum – On His Assuming the Pontificate, Pope Leo XII, 5 May 1824
- Quo Graviora: Condemning Secret Societies, 13 March 1826
- Charitate Christi: Extending Jubilee to the Entire Church, 25 December 1825
- Quod Hoc Ineunte: Proclaiming a Universal Jubilee, 24 May 1824
- Ad Plurimus easque Gravissimas, 1825
- Blessed Angelina di Marsciano
- Blessed Angelus of Acri
- Blessed Angelus of Gualdo Tadino
- Blessed Bernard Scammacca
- Blessed Constabilis of Cava
- Blessed Giovanna Soderini
- Blessed Helen Duglioli
- Blessed Helen of Poland
- Blessed Hippolytus Galantini
- Blessed Imelda Lambertini
- Blessed James Grissinger
- Blessed Jordan of Saxony
- Blessed Juana de Aza
- Blessed Julian of Saint Augustine
- Blessed Magdalen Panattieri
- Saint Alonso Rodriguez
- “Pope Leo XII“. CatholicSaints.Info. 10 April 2010. Web. 4 August 2015. <>