Canadian businessman and ornithologist. Born at Newton-on-Ayr and educated in Edinburgh, McIlwraith emigrated to Canada in 1853, settling in Hamilton (Ontario) where he managed the gas works. In 1871 he began in trade on his own account and was successful becoming a Director of several banks and insurance companies. He was also an Alderman of the City of Hamilton. An enthusiastic ornithologist, he became an expert on the birds of Ontario and published several papers on the subject, together with a well-received treatise the Birds of Ontario (1886). He was also a founder of the American Ornithologists' Union in 1883.
The McIlwraith Field Naturalists, an environmental club based in London (Ontario), which was established in 1864 was later renamed in his honour.