Robert Henry Preston (born March 15, 1840) was an Ontario doctor and political figure. He represented Leeds South from 1875 to 1879 and from 1883 to 1886 and Leeds from 1886 to 1894 in the Legislative Assembly of Ontario as a Conservative member.
He was born in Bastard Township, Leeds County in 1840, the son of Anthony Preston, a farmer who came to Upper Canada from Ireland. In 1862, he received an M.D. from Ann Arbor Medical College in Michigan; he went on to study at Bellvue College in New York and Queen's College and received his license to practice medicine in 1864, setting up practice in Newboro. In 1868, he was named associate coroner for the United Counties of Leeds and Grenville. Preston was president of the Brockville, Westport and Sault Ste. Marie Railway. He married Elizabeth, the daughter of Benjamin Tett, in 1868. He served as president of the North Crosby and Newboro Agricultural Association. Preston was also a member of the Freemasons.