He was the son of Bernardino Savelli, Duke of Castel Gandolfo and Lucrezia dei Conti dell'Anguillara.
In 1614 he appeared as Extraordinary nuncio in Piedmont, where he mediated in a dispute between King Philip III of Spain and Charles Emmanuel I, Duke of Savoy.
He was ordained Bishop on 10 April of the same year in the Roman church of Sant'Andrea in Montecavallo, the predecessor of Sant'Andrea al Quirinale, by Cardinal Scipione Borghese; co-consecrators were Archbishop Guido Bentivoglio, Apostolic Nuncio in France, and Antonio Grimani, Bishop of Torcello.
Following a nomination by King Philip IV of Spain, Giulio Savelli was appointed Archbishop of Salerno on 28 January 1630.
Giulio Savelli died in Rome and was buried in the family tomb in the church of Santa Maria in Ara Coeli.