American writer of realistic fiction, author of a major novel of the American Civil War—Miss Ravenel's Conversion from Secession to Loyalty (1867).

The son of a prosperous cotton manufacturer, DeForest did not go to college, owing to poor health, but traveled (1848–49) in the Middle East. He returned home to write a scholarly History of the Indians in Connecticut (1851) before setting out for Europe, where he lived from 1851 to 1854, reading widely in continental literature, particularly French. Two travel books came out of these experiences abroad: Oriental Acquaintance (1856) and European Acquaintance (1858).

When the American Civil War broke out, DeForest organized a company of New Haven volunteers and served as captain in the Federal campaigns in Louisiana and the Shenandoah valley. When the war was over, he was district commander of the Freedmen's Bureau in Greenville, S.C. (1866–67). His experiences in war and its aftermath, which he wrote about in detailed letters to his wife and in magazine articles, were published posthumously as A Volunteer's Adventures (1946) and A Union Officer in the Reconstruction (1948).

Two years after publication of Miss Ravenel's Conversion, he wrote a highly significant article, “The Great American Novel” (The Nation, Jan. 9, 1869), in which he called for a full-bodied realism in American fiction but said it was hard to achieve because American society was changing too rapidly to be comprehended as a whole.

His experiences in South Carolina were the basis of two novels: Kate Beaumont (1872), which depicts the social life of the state before the war; and The Bloody Chasm (1881), after the war. Two other novels deal with corruption in Washington, D.C., during the administration of President Ulysses S. Grant: Honest John Vane (1875) and Playing the Mischief (1875). His last novel, A Lover's Revolt (1898), is a romance of the American Revolution.