Willem de Fesch (, 1687, Alkmaar – 3 January 1761) was a virtuoso Dutch violone player and composer.
The pupil of Karel Rosier, who was a Vice-Kapellmeister at Bonn, de Fesch later married his daughter, Maria Anna Rosier.
De Fesch was active in Amsterdam between 1710 and 1725. From 1725 to 1731 he served as Kapellmeister at Antwerp Cathedral.
Thereafter he moved to London where he gave concerts and played the violone in Handel's orchestra in 1746. In 1748 and 1749 he conducted at Marylebone Gardens. He apparently made no public appearances after 1750.
His works included the oratorios Judith (1732) and Joseph (1746), as well as chamber duets, solo and trio sonatas, concertos and part songs. Both oratorios were thought lost until 1980 when a copy of a manuscript of "Joseph" was found in London's Royal Academy of Music.
De Fesch's music was influenced by the Italians, particularly Vivaldi, as well as Handel.