William Oscar Barnard (October 25, 1852 – April 8, 1939) was an American lawyer and politician who served one term as a U.S. Representative from Indiana from 1909 to 1911.

He taught school for five years in Henry and Wayne Counties.

He served as prosecuting attorney of the eighteenth and fifty-third judicial circuits from 1887 to 1893.

He served as judge of the fifty-third judicial circuit court of Indiana from 1896 to 1902.

This article incorporates public domain material from the Biographical Directory of the United States Congress