He was ordained to the priesthood on 1 June 1902 and then served as private secretary to his uncle, Cardinal Gaetano Aloisi Masella, the pro-datary of the pope.

Entering the Roman Curia, in the Secretariat of State, in 1906, Aloisi Masella then began work for the Nunciature to Portugal (secretary, 1908–1910; chargé d'affaires, 1910–1919).

Aloisi Masella received his episcopal consecration on the following 21 December from Cardinal Pietro Gasparri, with Archbishop Sebastião Leite de Vasconcellos and Bishop Antonio Maria Iannotta serving as co-consecrators.

On 27 October 1954, Pius XII appointed him archpriest of the Basilica of St. John Lateran and prefect of the Sacred Congregation for the Discipline of the Sacraments.

He was chosen chamberlain of the Roman Church (or camerlengo) on 9 October 1958 by the Curial cardinals, as the late Pius XII had yet to appoint anyone to that post, for the conclave of that same year.