Pellegrinetti served as a military chaplain during World War I, from 1917 to 1918, after which he was named secretary of the nunciature to Poland.

On 24 May 1922, Pellegrinetti was appointed Titular Archbishop of Adana by Pope Pius XI, and Nuncio to Yugoslavia a week later, on 29 May.

He also negotiated a concordat between Yugoslavia and the Vatican that the Yugoslav parliament did not ratify following riots that protested its indulgent stance towards Catholicism.

[1] Pope Pius made him Cardinal Priest of San Lorenzo in Panisperna in the consistory of 16 December 1937.

[2] Pellegrinetti was one of the cardinal electors who participated in the 1939 papal conclave, which selected Pope Pius XII.