Alfredo Pacini was born in Capannori and studied at the seminary in Lucca before being ordained to the priesthood on 25 July 1913.
He then did pastoral work in the Archdiocese of Lucca and taught at its seminary until 1915, when he became a military chaplain during World War I.
After resuming his work in Lucca, Pacini was raised to the rank of Honorary Chamberlain of His Holiness on 8 October 1924.
On 23 April 1946, Pacini was appointed Nuncio to Haiti and Santo Domingo and Titular Archbishop of Germia by Pope Pius XII.
Pope Paul VI made him Cardinal-Priest of Santi Angeli Custodi a Città Giardino in the consistory of 26 June 1967.