Robert Rainy (1 January 1826 – 22 December 1906), was a Scottish Presbyterian divine. Rainy Hall in New College, Edinburgh (the Divinity faculty in Edinburgh University) is named after him.
He was born in Glasgow, Scotland, the son of Dr Harry Rainy (1792-1876) Professor of Forensic Medicine in the University of Glasgow, and his wife Barbara Gordon (1793-1854). Young Rainy was intended for his father's profession, but instead returned to the path of his grandfather, Rev George Rainy (1734-1810) of Sutherland in northern Scotland. He was caught by the evangelical fervour of the Disruption movement, and after studying for the Free Church he became a minister, first in Aberdeenshire and then in Edinburgh, till in 1862 he was elected professor of Church history in the theological seminary, New College, a post he only resigned in 1900. In 1874 he was made principal of the college and was subsequently known as Principal Rainy. To this day, the dining Hall in New College is called the Rainy Hall.
He had come to the front as a champion of the liberal party in the Union controversy within the Free Church, and in combating Dean Stanley's Broad Church views in the interests of Scotch evangelicism; and about 1875 he became the undisputed leader of the Free Church. He guided it through the controversies as to Robertson Smith's heresies, as to the use of hymns and instrumental music, and as to the Declaratory Act, brought to a successful issue the union of the Free and United Presbyterian Churches, and threw the weight of the united church on the side of freedom of Biblical criticism.