William Harpin Mellor (June 6, 1874 – November 5, 1940) was a Major League Baseball first baseman.

In 10 career games, he had 13 hits in 36 at-bats, with 5 RBIs.

Mellor was born in Camden, New Jersey and died in Bridgeton, Rhode Island.

He served as the head baseball coach at Connecticut Agricultural College—now known as the University of Connecticut—for one season, in 1920.

This biographical article relating to an American baseball first baseman is a stub.