Marmaggi was ordained in Rome, on 14 April 1900, and afterwards worked in pastoral care in the Diocese of Rome, as well as being a faculty member of the Pontifical Roman Athenaeum Sant'Apollinare, and an official in the Apostolic Penitentiary until 1904. He was created Privy Chamberlain of PopePius X on 15 November 1907, and reappointed on 7 September 1914. Marmaggi was raised to the level of Domestic Prelate on 2 June 1915.
Marmaggi was made the second Nuncio to Czechoslovakia in 1923. Five years later, he was recalled to Rome as a sign of protest as a result of several disagreements on both sides, sparked by the Czechoslovak decision to continue celebrating the local festivalDen upálení mistra Jana Husa, which honored the 15th-century thinker Jan Hus, who influenced Protestant dogma and was burned at the stake as a heretic.[3][4][5]
Marmaggi left Prague on 6 July 1925, after repeatedly warning President Tomáš Masaryk, Premier Antonín Švehla and Foreign Minister Edvard Beneš not to attend the ceremonies.[4][5] They reportedly argued that they were participating as private persons.[5] Marmaggi's protest was echoed by the Catholic People's Party, which criticized Masaryk.[4] As a result of Marmaggi's departure, Czechoslovakia cut diplomatic ties with the Holy See.[4]
Marmaggi participated in the conclave of 1939 that elected Pius XII. He left Poland in March 1939, when he was appointed cardinal and Prefect of the Congregation of the Council. Reportedly, he wanted his successor in Poland to be Angelo Giuseppe Roncalli, the Nuncio to Turkey and Greece and future Pope John XXIII.[7]
Marmaggi was Prefect until his death in 1949. A street in Rome was named in his honor "Via Cardinale Marmaggi".