William Nelson was born on September 27, 1824 in Maysville, Kentucky, United States. He was the youngest son of Dr. Thomas W. Nelson and Frances (Doniphan) Nelson. His elder brothers were Anderson Doniphan Nelson, who became an army officer, and Thomas Henry Nelson.
Nelson attended Maysville Academy (Seminary) and was enrolled in Norwich University at age thirteen.
William was appointed midshipman in the United States Navy on January 28, 1840, and became passed midshipman July 11, 1846. He served with the fleet which supported Scott's invasion of Mexico and commanded a battery during the siege of Vera Cruz, March 9-29, 1847. Later he served with the Mediterranean Squadron and on board the Niagara when that ship was used to return to Africa the slaves taken from the slaver Echo. He was promoted master in September 1854 and lieutenant, April 18, 1855.
During the spring of 1861, Nelson, who was devoted to the Union, made several visits to his native state to study conditions there, reporting his observations to the President, who in April sent him into Kentucky to arm the loyalists and to organize regiments for the Union Army. Some five thousand stand of arms were distributed to the Kentucky Home Guard, the Unionist military organization of the state.
Early in August, Nelson established Camp Dick Robinson in Garrard County and began to organize troops for an expedition into East Tennessee. He was commissioned brigadier-general of volunteers, September 16, 1861, and later in the fall was sent into Eastern Kentucky to supervise recruiting camps. During November he expelled a small Confederate column which had invaded the state. Later he joined Buell's Army of the Ohio before Louisville and was given command of the 4th Division. He marched with Buell's command to Pittsburgh Landing. Nelson's division was the first element of the Army of the Ohio to arrive on the field of Shiloh. He reached the battlefield with his leading brigades about 5:00 P. M. , April 6, 1862, and checked the victorious Confederate advance near the river bank. He bore an important part in the Union counterattack on April 7 and participated in the occupation of Corinth, Mississippi. After Corinth, he participated in the advance against Chattanooga. On July 17, 1862, he was commissioned major-general of volunteers. In that month he was ordered, with his division, to Nashville to protect Buell's communications against raid by Forrest's Confederate cavalry. When the Confederate armies of Bragg and E. Kirby-Smith invaded Kentucky, Nelson was sent thither to organize troops.
On August 30, he was wounded at Richmond, Kentucky, while attempting to rally two of his brigades which had been severely defeated. Later he was placed in command at Louisville to organize its defense. While thus engaged, he had occasion to reprimand Brigadier general Jefferson C. Davis for alleged negligence. A few days later, September 29, 1862, Davis, in company with Governor O. P. Morton of Indiana, encountered Nelson in the lobby of the Galt House in Louisville. During the altercation which ensued, Davis shot Nelson, who died in about half an hour.
His untimely death lost a valuable officer to the Union cause.
Nelson was a strong and dominating character, of great energy, a strict disciplinarian, and intolerant of neglect of duty.
