William Josiah MacDonald (November 17, 1873 – March 29, 1946) was a politician from the U.S. state of Michigan.

In 1912, MacDonald ran as a candidate for the Progressive Party against incumbent Republican H. Olin Young to the United States House of Representatives from the Michigan's 12th congressional district.

Although unofficial returns showed that MacDonald had won the seat, some votes were not included in the official count by the state board of canvassers due to a mistake in how MacDonald's name appeared on the ballot in Ontonagon County.

[1][2] H. Olin Young presented credentials as a Member-elect to the 63rd United States Congress and served from March 4, 1913, until his resignation, effective May 16, 1913, while a contest for the seat was pending.

MacDonald and Roy O. Woodruff (10th district) were the only two Michigan residents elected to the U.S. House from the Progressive Party.