Forbes was born in New York City and began studying art in 1857 with Arthur Tait who specialized in painting action scenes of scouts and Indians on the Western Plains. Later in his career, Forbes returned to painting and focused on depicting landscapes and animals. His career as an illustrator began in 1861 when he became a staff artist for Frank Leslie’s Illustrated Newspaper and was sent to cover the campaigns of the Army of the Potomac. He followed the Union Army from Cross Keys in the Shenandoah Valley to the battles at Manassas in 1862 and the siege of Petersburg in 1864. He made quick sketches on the battlefields then refined these later. He had a strategic viewing spot to observe Pickett’s charge at Gettysburg, and he was the first of the “special artists” to produce drawings of the battle to send back to Leslie’s in New York. He was most interested in capturing scenes of camp life. Leslie’s published 178 of his wartime drawings. In 1864, Forbes resigned his position at Leslie’s but continued to produce images of war. Many of these drawings were made into copper plate etchings and published as Life Studies of the Great Army (1876) for which he was awarded a medal at the Philadelphia Centennial in 1876. General William T. Sherman purchased the first proof and donated it to the United States government. Forbes’s illustrations also appeared in Beyond the Mississippi (Hartford, 1869), which contained drawings from photographs and earlier published prints of scenes from the Mississippi to the Pacific coast by many of the Civil War artists including Joseph Becker, Alfred Waud, William Waud, Frank Schell, and Thomas Nast. Forbes also did illustrations for numerous publications including Pebbles and Pearls for Young Folks (Hartford, 1868), Specimen Pages and Illustrations from Appleton’s Journal (New York, 1870), The Atlantic Almanac (1871), and School Days at Mount Pleasant by Ralph Morley (New York, 1872). In 1878 he opened a studio in Brooklyn, and in 1890 he published a summary of his work in Thirty Years After: An Artist’s Story of the Great War. The Becker Collection contains drawings done by Forbes in Virginia between 1862 and 1863.