He was a boy chorister at Cappella Giulia under Giovanni Pierluigi da Palestrina. He served at two Roman churches: Santa Maria in Monserrato and Santissima Trinità dei Pellegrini. Maestro di cappella of the Collegio Germanico (from 1595), he held the same position at S Pietro from 1602, but he left the post to Francesco Soriano from 1 January 1603; in the same year Pacelli became Maestro di cappella of King Sigismund III of Poland, who had one of the most important royal chapels in Europe.Luca Marenzio, Marco Scacchi and Giovanni Francesco Anerio were musicians at the same court. He remained at that position until his death. In appreciation, the King ordered an epitaph commemorating Pacelli to be constructed in the St. John's Cathedral in Warsaw. The original epitaph with the composer's portrait was destroyed when the Cathedral was also destroyed during the Planned destruction of Warsaw; it was nonetheless reconstructed after the war.
