Born in York, Pennsylvania on February 27, 1823. His father, Walter, was Clerk of the United States House of Representatives from 1833-1838 and a grandfather was a member of the First Continental Congress. His mother was Sarah Buell.

Senator and future President James Buchanan appointed Walter to the United States Military Academy. He graduated in 1843, first of his class of 39, which included his good friend Ulysses S. Grant. His top ranking earned him an appointment to the Topographical Engineers.

Franklin spent two years on a survey expedition in the Rocky Mountains before returning to administrative duty in Washington. With the outbreak of the Mexican War he served with Philip Kearny, earning a brevet promotion to first lieutenant at Buena Vista.

After the war he returned to West Point for three years as Assistant Professor of Natural and Experimental Philosophy. In January of 1851 he was assigned to building lighthouses and custom-houses along the Maine and New Hampshire coast. In July of 1852 he married Anna L. Clark, whose father had also been Clerk of the House.

In March of 1857 Franklin took over all U.S. lighthouse construction as supervisor of the Light House Board, and in November he was promoted to captain. In November of 1859 he came to Washington and was appointed supervising engineer on the construction of the Capitol Dome. In March of 1861 he became supervising architect on the Treasury Building.

On June 18,1861 Franklin was appointed colonel of the newly reconstituted 12th United States Infantry (to date from May 14). He commanded the 1st Brigade in Heintzelman’s Division at Bull Run, and on August 20 he was appointed Brigadier General of United States Volunteers (to date from May 17). In October of 1861 he was given command of a division which became part of McDowell’s 1st Army Corps in March of 1862.

In April of 1862 the First Corps was detached from the Army of the Potomac and was designated the Department of the Rappahanoock. But on May 18 Franklin’s division was returned to the Army of the Potomac and became the nucleus for the new Sixth Army Corps, commanded by Franklin. On June 30, 1862 he was brevetted brigadier general in the Regular Army and on July 4 he was promoted to major general of United States Volunteers.

Franklin commanded the Sixth Corps at South Mountain, where he overwhelmed Confederate defenders at Crampton’s Gap but was too slow to save the besieged Union garrison at Harpers Ferry, and at Antietam, where he unsuccessfully tried to convince Major General Edwin Sumner to resume the attack on the Confederate left flank after Hooker was wounded.

Franklin was given command of the Left Grand Division of the Army of the Potomac under Burnside, which included the First Army Corps as well as his Sixth Corps, now under Major General William F. Smith. After Burnside unjustly blamed Franklin for the disaster at Fredericksburg, Franklin was one of the leaders in the group that formed to remove Burnside from command. Although successful in forcing Burnside from the Army of the Potomac, Franklin lost his command as well.

Franklin returned to the field in June of 1863 in the Department of the Gulf, where he commanded a corps in Nathaniel Banks’ unsuccessful Red River Campaign. Franklin was wounded at the Battle of Mansfield on April 8, 1864, and while returning home to recuperate was captured by Confederate raiders on a train near Baltimore. He escaped that night and wandered for two days before hunger drove him to a farmhouse. Fortunately, it belonged to a Union sympathizer who sent word to Baltimore, and a large force was sent to Franklin’s rescue.

Franklin served on several boards and in March of 1865 was brevetted major general in the Regular Army, but he never again was given high command.

After the war Franklin moved to Hartford, Connecticut and became the Vice President and General Manager of the Colt Patent Fire Arms Company. He put his engineering expertise to work supervising the building of the Connecticut State Capitol and served for 15 years on the city board of water commissioners. He became Vice President of the Hartford Steam Boiler Inspection & Insurance Company and a director of the Connecticut Mutual Life Insurance Comany.

Franklin turned down an invitation to run for President against his friend and classmate Grant in 1872, but was a delegate to the 1876 Democratic National Convention. From 1877 to 1879 he was Connecticut’s Adjutant General.

Anna Franklin died in July of 1900, and William died in Hartford, Connecticut on March 8, 1903. They had no children. They are buried in Prospect Hill Cemetery in York, Pennsylvania.