He was born in Derby, Connecticut and graduated from Yale in 1772, studied law in Litchfield, Connecticut and passed the bar in 1775.
At the outbreak of fighting in the American Revolution, Hull joined a local militia and was quickly promoted to captain, then to major, and to lieutenant colonel. He was in the battles of White Plains, Trenton, Princeton, Stillwater, Saratoga, Fort Stanwix, Monmouth, and Stony Point. He was recognized by George Washington and the Continental Congress for his service.
Hull was a friend of Nathan Hale and tried to dissuade Hale from the dangerous spy mission that would cost him his life. Hull was largely responsible for publicizing Hale's famous last words, "I only regret that I have but one life to lose for my country." After the American Revolution, he moved to his wife's family estate in Newton, Massachusetts and served as a judge and state senator in Massachusetts.
On March 22, 1805, President Thomas Jefferson appointed him Governor of the recently-created Michigan Territory as well as its Indian Agent. As almost all of the territory except for two enclaves around Detroit and Fort Michilimackinac were in the hands of the Indians, Hull undertook the goal of gradually purchasing more Indian land for occupation by American settlers. He negotiated the Treaty of Detroit with the Ottawa, Chippewa, Wyandot and Potawatomi nations, which ceded most of present-day Southeast Michigan to the United States. These efforts to expand American settlement began to generate opposition, particularly from the Shawnee leaders Tecumseh and his brother Tenskwatawa, the Shawnee Prophet, who preached resistance to the American lifestyle and to further land giveaways.
By February 1812, the US was openly talking about and making plans in Congress for war with Great Britain, including an invasion of Canada. The British responded by recruiting Native American tribes to form part of their defence in the Michigan, Canada area in case the Americans attacked Canada. While Hull was in Washington, Secretary of War William Eustis informed him that President Madison wished to appoint him a Brigadier General in command of the new Army of the Northwest. Hull, then nearly 60 years old, expressed his disinterest in a new military commission, and a Colonel Kingsbury was selected to lead the force instead. Kingsbury fell ill before taking command, and the offer was repeated to Hull, who this time accepted. His orders were to go to Ohio, whose governor had been charged by Madison with raising a 1,200-man militia that would be augmented by the 4th Infantry Regiment from Vincennes, Indiana, to form the core of the army. From there he was to march the army to Detroit, where he was to also continue serving as Territorial Governor.
Hull arrived in Cincinnati on May 10, 1812, and on May 25 took command of the militia at Dayton. The militia comprised three regiments, who elected as their commanding Colonels Duncan McArthur, Lewis Cass, and James Findlay. They marched to Staunton and then to Urbana, where they were joined by the 300-man 4th Infantry Regiment. The men of the militia were ill-equipped and lacked military discipline, and Hull relied on the infantry regiment to quell several instances of insubordination on the remainder of the march. By the end of June, the army had reached the rapids of the Maumee River, where Hull committed the first of the errors that would later reflect poorly on him.
The declaration of war on Great Britain was signed on June 18, 1812, and that same day Secretary Eustis sent two letters to General Hull. One of them, sent by special messenger, had arrived on June 24 but did not contain any mention of the declaration of war. The second one, announcing the declaration of war, was sent via the postal service, and did not arrive until July 2. As a result, Hull was still unaware that war had broken out when he reached the rapids of the Maumee, and as the army was now on a navigable waterway, he sent the schooner Cuyahoga Packet ahead of the army to Detroit with a number of invalids, supplies, and official documents. Unfortunately for Hull, the British commander at Fort Amherstburg had received the declaration of war two days earlier, and captured the ship as it sailed past, along with all of the papers and plans for an attack on Fort Amherstburg.
Hull was, at least in part, the victim of poor preparation for war by the U.S. government and miscommunication. While governor, Hull's repeated requests to build a naval fleet on Lake Erie to properly defend Detroit, Fort Mackinac, and Fort Dearborn were ignored by the commander of the northeast, General Henry Dearborn. Hull began an invasion of Canada on July 12, 1812. However, he quickly withdrew to the American side of the river after hearing the news of the capture of Fort Mackinac by the British. He also faced unfriendly Native American forces, which threatened to attack from the other direction.
Facing what he believed to be superior forces thanks to his enemy's cunning stratagems such as instructing the Native American warriors to make as much noise as possible around the fort, Hull surrendered Fort Detroit to Sir Isaac Brock on August 16, 1812. Accounts of the incident varied widely. A subordinate, Colonel Lewis Cass placed all blame for the surrender on Hull and subsequently succeeded Hull as Territorial Governor. Hull was court-martialed, and at a trial presided over by General Henry Dearborn, with evidence against him given by Robert Lucas, a subordinate and the future governor of Ohio and territorial governor of Iowa. Hull was sentenced to be shot, though upon recommendation of mercy by the court, Hull received a reprieve from President James Madison.
Hull lived the remainder of his life in Newton, Massachusetts and wrote two books attempting to clear his name (Detroit: Defence of Brig. Gen. Wm. Hull in 1814 and Memoirs of the Campaign of the Northwestern Army of the United States: A.D. 1812 in 1824). Some later historians have agreed that Hull was unfairly made a scapegoat for the embarrassing loss. The publication of his Memoirs in 1824 changed public opinion somewhat in his favor, and he was honored with a dinner in Boston on May 30, 1825. That June, Lafayette visited Hull and declared, "We both have suffered contumely and reproach; but our characters are vindicated; let us forgive our enemies and die in Christian love and peace with all mankind." Hull died at home in Newton several months later, on November 29, 1825.
He was also uncle to Isaac Hull and adopted Isaac after his father (William's brother Joseph) died while Isaac was young.