His father, who died when Williams was eight years old, had left him a sizable inheritance, which he used between 1832 and 1836 for extensive travel in the United States and Europe.

He established himself as a lawyer and married the daughter of a prominent family, Jane Hereford Larned, with whom he produced five children, two of whom died as infants.

When Williams arrived in Detroit in 1836, he joined a company in the Michigan Militia and maintained a connection to the military activities of the city for years.

In 1847, he was appointed lieutenant colonel of the 1st Michigan Infantry destined for the Mexican–American War, but it arrived too late to see any action.

His first assignment after leaving the training camps was as a brigade commander in Maj. Gen. Nathaniel Banks's division of the Army of the Potomac, from October 1861 to March 1862.

George McClellan assigned Maj. Gen Henry Slocum permanent command of the XII Corps after the battle.

The neighboring division, under Williams, entrenched hastily and was able to stop the Confederate advance before it overran the entire army, but it suffered 1,500 casualties in the process.

Williams convinced Meade of the importance of Culp's Hill and managed to retain one brigade, under Greene, in their defensive positions.

Early on July 3, Williams launched an attack against the Confederates who had occupied some of the entrenchments on the hill and, after a seven-hour battle, regained his original line.

During the Battle of Chancellorsville, a Confederate shell landed in the thick mud underneath Plug Ugly.

[1] After the war, Williams served as a military administrator in southern Arkansas until he left the service on January 15, 1866.

He returned to Michigan, but faced financial difficulties that forced him to take a post as the U.S. Minister at San Salvador, a position in which he served until 1869.

Williams was elected as a Democrat to the 45th United States Congress from Michigan's 1st congressional district, serving from March 4, 1875, to December 21, 1878.

There were three reasons likely for the situation: first, he was not a West Point graduate, and the "old boys network" was as effective in the 19th century as it is today; second, during the formative months of the Army of the Potomac, Williams was stationed in the Shenandoah Valley, which denied him familiarity to the high command when reputations were being established; third, Williams was never comfortable mastering the common practice of promoting himself to the public with the help of friendly newspaper correspondents.

[citation needed] An equestrian memorial to Williams by sculptor Henry Shrady stands in Belle Isle Park, in his home town of Detroit.