Giacomelli was born in Piacenza. In 1724 he was named to the post of Kapellmeister to the duke of Parma. Beginning with the first performance of his opera Ipermestra, in 1724, he became one of the most popular opera composers of his era. Between 1724 and 1740 he composed 19 operas, and for many years worked at the Imperial Court in Vienna. His best known opera is Cesare in Egitto of 1735. He also wrote a deal of sacred music, including eight psalm settings for tenor and bass, and some concertos with continuo. In 1738 Giacomelli again became Kapellmeister, this time at the Basilica della Santa Casa in Loreto; he died in Loreto in 1740.