Two years later, Naumann's Li creduti spiriti, composed for the Venetian carnival in collaboration with two other composers, secured the endorsement of Hasse and Ferrandini, both of whom recommended him for a post as second church composer in Dresden. There, Naumann was soon promoted to chamber composer in 1765. Subsequently, he decided to return to Italy for three years, where he composed his opera La clemenza di Tito, staged in Dresden in 1769. Naumann's next stay in Italy between 1772 and 1774 further consolidated his reputation as a major operatic composer. He was finally appointed Kapellmeister at Dresden in 1776.
In 1777, the Swedish ambassador Count Lowenhjelm asked him to travel to Stockholm, where he assisted King Gustavus III in re-forming the Hovkapell. He also composed operas for the Swedish court, many of which were tremendously successful. The finest, Cora och Alonzo, was staged for the inauguration of the Royal Opera House. In 1782, Gustavus III commissioned a Swedish nationalist opera, Gustaf Wasa, which received its premiere in 1786 and remained Sweden's most popular opera for over a century, with more than 250 performances.
In 1785, Naumann guested as opera composer and conductor for the Danish court and reorganized the opera at Copenhagen. He would not commit to an extended contract there, however, and returned to Dresden, becoming Oberkapellmeister. In 1792, he married Catarina von Grodtschilling, daughter of a Danish vice-admiral, and although during his final years he contemplated a German national opera based on his experiences in Scandinavia, it never materialized.