Pietro Marini was born in 1794 in Rome, in what was then the Papal States. He was the son of Neapolitan architect Francesco Saverio Marini and Irene De Dominicis. Marini was baptised in the patriarchal Vatican basilica in 1794; his godfather was Cardinal Gregorio Barnaba Chiaramonti, O.S.B.Cas., the futurePope Pius VII. Marini is an ancestor of Cardinal Niccolò Marini. Marini studied letters and philosophy at the Pontifical Roman Seminary from 1804 to 1810; then, at La Sapienza University, Rome, obtaining a doctorate ad honoremin utroque iure on 24 July 1816. He also obtained the title of advocate at the Roman Curia. Marini served as a civil assessor of the province of the Romagna from 1817 to 1820; before being named patrician of Ravenna by the city in 1820. He received the ecclesiastical tonsure in 1821. After this he became referendary of the Tribunals of the Apostolic Signatura of Justice and of Grace on 9 September 1821. He was created Domestic prelate of His Holiness. From March 1822 he served as a relator of the Sacred Congregation for Good Government. He was also a member of the Congregation of the Fabric of Saint Peter's Basilica. He served as auditor of Cardinal CamerlengoBartolomeo Pacca from 1823 to 1824. He was an honorary member of the literary Academy of San Luca from 1824, a voting member of the Tribunal of the Apostolic Signature of Justice, 1824-1825, an Auditor of the Apostolic Chamber, and Auditor of the Sacred Roman Rota. He was appointed governor of Rome, vice-camerlengo of the Holy Roman Church and director general of police on 22 April 1845, serving until 21 December 1846. He was ordained to the priesthood on 27 May 1844. On 21 December 1846 he was made a Cardinal-Deacon, receiving the galero on 23 December 1846 and being given the deaconary of San Nicola in Carcere on 12 April 1847. His cardinalitial motto was Ne quid nimis. Cardinal Marini served as apostolic legate in the province of Forlì, Prefect of the economy of the Sacred Congregation of Propaganda Fide and president of the Camera degli Spoglie, Protector of the city of Urbino, Protector of the city of Forlimpopoli, Prefect of the Tribunal of the Signature of Justice, Protector of the city of Fabriano. He resided in the Collegio San Carlo ai Catinari. He died on 19 August 1863 in Rome. After lying in state in the church of San Carlo ai Catinari, the funeral took place on 24 August 1863, with Pope Pius IX participating. He is buried in his deaconry of San Nicola in Carcere.
