William Candidus (23 July 1840 in Philadelphia – April 1910 in Frankfurt am Main) was an American opera singer.

During the American Civil War, he served three years in the 2nd Pennsylvania Heavy Artillery and elsewhere, being advanced to the grade of major.

During his military service his voice gradually changed from first bass to tenor.

After his return from the war, he accepted the position of tone regulator in the piano factory of Steinway & Sons, in New York City.

He became a member of the Arion and Liederkranz societies, but soon went abroad and studied for the operatic stage under Konapazeck (Konaptczek) of Berlin, making his début in Weimar as Stradella.