Joseph Ferdinand Sonnleithner (3 March 1766 – 25 December 1835) was an Austrian librettist, theater director, archivist and lawyer.

Sonnleithner began working for the Viennese court in 1787, first at Joseph II's private office and later in the chancellery.

[2] He was also a leading figure in Viennese musical life in the first decades of the nineteenth century and consequently one of the founders of the Gesellschaft der Musikfreunde, serving as its first secretary starting in 1812.

[n 1] Sonnleithner was one of the earliest collectors of folksongs and information on their composers in Austria, a project which, though never fulfilled, formed the basis of a new musical encyclopedia.

For his treasured collection of oil paintings from the Baroque period on,[3] which is now kept in the Gesellschaft der Musikfreunde, he also commissioned a special portrait of Schubert from the artist Anton Depauly.