Antonetti studied at the seminaries in Novara and Rome, the subjects of Catholic theology and philosophy, he was a seminarian at the Almo Collegio Capranica and received in 1945 the sacrament of Holy Orders. He then worked for two years as a parish pastor in his home diocese. From 1947 to 1951 he continued his studies and graduated from high school to study theology at the Pontifical University of Saint Thomas Aquinas ( Angelicum ). At the Pontifical Gregorian University, he received his doctorate in canon law.
In 1949 he entered the diplomatic service of the Holy See and was trained at the Pontifical Ecclesiastical Academy. From 1951 he worked for the Vatican Secretariat of State. From 1952 to 1955 he was attaché and secretary of the Apostolic Nunciature in Beirut, Lebanon, from 1955 to 1959, he provided the same task at the Nunciature in Caracas, Venezuela. In the years 1959 to 1963 he was employed in the Department of Special Affairs of the Vatican Secretariat of State. Further international career took him as a counselor to Paris, France and Washington, DC, USA.
On February 23, 1968 Pope Paul VI appointed him. Titular Archbishop of Rusellae and Apostolic Nuncio of Honduras and Nicaragua. He received his episcopal consecration Cardinal Secretary of State Amleto Giovanni Cicognani on May 12 of the same year. From 1973 to 1977 he was Pro-Nuncio in Kinshasa, Zaire. From 1977 to 1988 he worked as secretary of administration of goods of the Apostolic See APSA, which was at that time under the direction of the Cardinals Villot, Caprio, Casaroli and Rossi. He was among other things responsible for the liquidation of the Pontificia Opera di Assistenza (POA ) and Opera Nazionale Assistenza religiosa e Morale agli Operai ( ONARMO ). He was president of Fondo Assistenza Sanitaria (FAS ), a member of the Disciplinary Commission of the Roman Curia, the Pontifical administration of the Papal Basilica of Saint Paul Outside the Walls and responsible for the spread of the new Code of Canon Law in 1983.
In 1988 he was appointed by Pope John Paul II, Apostolic Nuncio to France. On 24 June 1995, the appointment as Pro- President of the estate management of the Apostolic See APSA was.
On February 21, 1998, Pope John Paul II was a cardinal deacon with the Titelkdiakonie S. Agnese in Agnone in the College of Cardinals to. From 23 February to November 5, 1998 Antonetti was president of administration of goods of the Apostolic See APSA. From 1998 to 2006 he was papal delegate for the Basilica of San Francesco in Assisi.
At the conclave after the death of Pope John Paul II in 2005, he no longer took part because he had the age of 80 years already passed.
On 1 March 2008 it rose Benedict XVI. cardinal priest per hac vice.
Cardinal Antonetti also no longer participated in the conclave of 2013. He died four weeks after the election of Pope Francis.