William MacGillivray was a Scottish naturalist and ornithologist.

MacGillivray was born in Old Aberdeen and brought up on Harris. He returned to Aberdeen where he studied Medicine at King's College, graduating MA in 1815. In Old Aberdeen he lived at 107 High Street.

He then became an assistant Dissector in the Anatomy classes. In 1823 he became assistant to Robert Jameson, the Regius Professor of Natural History at the University of Edinburgh. He was curator of the museum of the Royal College of Surgeons of Edinburgh from 1831, resigning in 1841 to become Regius Professor of Natural History at Marischal College, Aberdeen.

MacGillivray was a friend of American bird expert John James Audubon, and wrote a large part of Audubon's Ornithological Biographies from 1830 to 1839. Audubon named MacGillivray's warbler for him.

He died at 67 Crown Street in Aberdeen on 5 September 1852 but is buried in New Calton Cemetery in Edinburgh. The grave faces east onto the eastern path.