| Type: | Cardinal |
| Honorific Prefix: | His Eminence |
| Mario Mattei | |
| Dean of the College of Cardinals | |
| Church: | Roman Catholic Church |
| Appointed: | 30 September 1860 |
| Term End: | 7 October 1870 |
| Predecessor: | Vincenzo Macchi |
| Successor: | Costantino Patrizi Naro |
| Ordination: | c. 1817 |
| Consecration: | 23 June 1844 |
| Consecrated By: | Vincenzo Macchi |
| Cardinal: | 2 July 1832 |
| Created Cardinal By: | Pope Gregory XVI |
| Rank: | Cardinal-Deacon (1832–42) Cardinal-Priest (1842–44) Cardinal-Bishop (1844–70) |
| Birth Name: | Mario Mattei |
| Birth Date: | 6 September 1792 |
| Birth Place: | Pergola, Marche |
| Death Place: | Rome, Kingdom of Italy |
| Buried: | Saint Peter's Basilica |
| Parents: | Marco Mattei Francesca Orsini Bianchi |
Mario Mattei (6 September 1792, Pergola, Marche – 7 October 1870) was an Italian Cardinal, of the Roman noble House of Mattei. He became Dean of the College of Cardinals in 1860.
Mario Mattei was born on 6 September 1792 in Pergola, Marche.
He was educated at the Collegio Ghislieri, a Roman college, and at the La Sapienza University where he received a doctorate in utroque iure) and later attended the Pontifical Academy of Ecclesiastical Nobles in 1810.[1] Around 1817, he was ordained a priest.
He was elevated to Cardinal by Pope Gregory XVI in 1832 and was subsequently appointed to the following posts:[2]
In 1843, Mattei was appointed as Arch-Priest of St. Peter's Basilica and held this position until his death in 1870.
Records indicate that Mattei was appointed Camerlengo of the Sacred College of Cardinals twice; between 1834 and 1835 and between 1848 and 1850 and he was also appointed to be the Dean of the College of Cardinals in 1860. He was a participant in the First Vatican Council between 1869 and 1870 and in the Papal Conclave of 1846 that elected Pope Pius IX.