William Rathbone Greg (1809 – 15 November 1881) was an English essayist.
Born in Manchester, the son of Samuel Greg, the creator of Quarry Bank Mill, he was brother to Robert Hyde Greg and the junior Samuel Greg. He was educated at the University of Edinburgh. For a time, he managed a mill of his father's at Bury, and in 1832 began business on his own account. He entered the struggle for free trade, and obtained in 1842 the prize offered by the Anti-Corn Law League for the best essay on Agriculture and the Corn Laws. He was too busy with political, economical and theological speculations to give undivided attention to his business, which he gave up in 1850 to devote himself to writing. His Creed of Christendom was published in 1851, and in 1852 he contributed no less than twelve articles to four leading quarterlies. Disraeli praised him. Sir George Cornewall Lewis bestowed a Commissionership of Customs on him in 1856. In 1864 he was made Comptroller of the Her Majesty's Stationery Office.
He became a member of the Metaphysical Society. Besides contributions to periodicals he produced several volumes of essays on political and social philosophy. The general spirit of these is indicated by the titles of two of the best known, The Enigmas of Life (1872) and Rocks Ahead (1874). They represent a reaction from the high hopes of the author's youth, when wise legislation was assumed to be a remedy for every public ill. Greg was a man of deep moral earnestness of character and was interested in many philanthropic works. He died at Wimbledon, London.
One son, Percy Greg, was also a writer; another, Walter Wilson Greg, was a leading bibliographer of Renaissance drama.