William Franklin was born in York, Pennsylvania, on 27th February, 1823. He graduated first in his class of 39 from West Point in 1843. He fought in the Mexican War where he won two brevets. A specialist engineer, Franklin supervised several construction projects and taught the subject at the U.S. Military Academy.

On the outbreak of the American Civil War Franklin joined the Union Army and was named colonel of the 12th Infantry. He took part in the battles at Bull Run (June, 1861) and Antietam (September, 1862). Franklin led the Left Grand Division at Fredericksburg (November, 1862). Afterwards his performance at the battle was criticized by General Ambrose Burnside and the Committee on the Conduct of the War.

Franklin was wounded and captured at Sabine Cross Roads on 11th July, 1864 by a force led by General Jubal A. Early. He later escaped but did not return to active service. In 1866 he retired from the United States Army and was appointed as vice-president of the Colt's Fire Arms Manufacturing Company and over the next few years was employed by several companies as a consulting engineer.

William Franklin died in 1903.