William Hennessy may refer to:
Bill Hennessy (Cork hurler) (1882–1954) Bill Hennessy (Kilkenny hurler) (born 1968) William Hennessy (violinist), Australian classical violinist William C. Hennessy, American civil servant and political figure William J. Hennessy Jr., American court sketch artist William John Hennessy, Irish artist William Maunsell Hennessy, Irish official and scholar