Rosecrans was the son of Crandell Rosecrans and Jane Hopkins, whose grandfather was Stephen Hopkins, colonial Governor of Rhode Island and a signer of the Declaration of Independence. Hopkins also co-authored the draft of the Articles of Confederation with John Adams.
Rosecrans graduated from West Point in 1842, ranked 5 out of 56 in his class.
He was appointed a 2d lieutenant in the Corps of Engineers. Later, he served as an instructor at West Point, and supervising construction in the New England area. He resigned from the army in 1854 to become a civil engineer, architect, and coal and oil refiner. He took over a mining business in western Virginia and ran it successfully. He was also an inventor. Numbered among his inventions were odorless oil, a round lamp wick, a short practical lamp chimney, and a new and economical method of manufacturing soap.
While president of the Preston Coal Oil Company in 1859, an oil lamp exploded, burning Rosecrans severely. He was bedridden for 18 months recovering from the burns. As he finished recovering, the Civil War began.
He began service as a volunteer aide-de-camp to Major Gen. George B. McClellan. Promoted to the rank of Colonel, he took up the command of the 23rd Ohio Volunteer Infantry. Soon, he received promotion to Brigadier General. His plans and decisions proved extremely effective in the West Virginia Campaign, including the Union victory at Rich Mountain, of which McClellan received the credit. McClellan did not give him any credit in the official reports, thus, he refused to go east with McClellan and requested a transfer to the West.
Rosecrans received the command of the left wing of the Army of the Mississippi, fighting at both Iuka and Corinth. He became known as the Union's "fighting general" when he defeated the Confederate armies. After Corinth, animosities between Lieutenant Gen. Ulysses S. Grant and Rosecrans arose. Grant blamed him for not pursuing the Confederate army after Corinth and he placed blame on Grant for not sending reinforcements during and immediately after the battle.
Nonetheless, he assumed command of XIV Corps and was promoted to major general of volunteers.
In this corps command, Rosecrans battled against Gen. Braxton Bragg in the Union victory at Stones River. He then reorganized his corps into a separate command, the Army of the Cumberland. The costly and non-decisive battle seemed to have changed his life and sapped his will to fight. The bloody realities of war continued to take their toll on him. He reacted by becoming worrisome, hesitant, and cautious and for months. Finally, he left for the Tullahoma Campaign.
Rosecrans became one of the most well-liked generals in the Union Army. He was loved by the his men but was harsh on his officers. A very problematic fault of his was that once a battle began, he became very excitable which led him to stutter and become very difficult to understand. Another problem was that he would micro-manage the movements of units himself instead of using the chain-of-command to direct movements. These problems were never more apparent than at Chickamauga.
On September 8, 1863, Rosecrans's army forced the Confederates out of Chattanooga without firing a shot. But then, abandoning his usual caution, he took part of his force and pursued the Confederates southward. By September 18, the Confederate army had been reinforced and was ready to take the offensive. He saw this and began to retreat to Chattanooga, but the Confederates attacked at Chickamauga.
On the third day of the battle, He issued an order to one of his generals "to close in and support his left." This order created a weak point in the Union lines in the Union line which coincided with Lieutenant Gen. James Longstreet's attack, forcing most of the Union army into a disorderly retreat. This led to the Confederate victory. Back in Chattanooga, he was slow to recover from the beating he had taken and seemed unable to regain his confidence. President Abraham ordered Grant to dismiss him from command. He relieved of his command from the Army of the Cumberland.
Rosecrans went to Cincinnati to await further orders, but ultimately he would play no further large part in the fighting. He would eventually be given command of the Department of Missouri until war's end, where he was active in opposing Major Gen. Sterling Price's Missouri Raid. He spent more than 2 years without a command, then resigned from the army in 1867.
After the war, President Andrew Johnson appointed Rosecrans as U.S. Minister to Mexico from 1868-69 , but was replaced when Grant became president. He returned to private mining business in Mexico and California for 10 years. He was elected to the U.S. Congress from California, serving from 1881-85. President Grover Cleveland appointed him Registrar of the U.S. Treasury Department from 1885-93.
After Rosecrans died, he was buried at Arlington National Cemetery. He was 1 of 15 Army officers given the Thanks of Congress during the Civil War. His was for the actions at Stones River.
Lieutenant Colonel -
Brigadier General USA- May 16, 1861
Major General USV- March 21, 1862
Major General USA- March ??, 1865 (brevetted for Stones River)
Aide de Camp/Colonel of Engineers (April 23- June 12, 1861)
23rd Ohio Volunteer Infantry (June 12- 17, 1861)
Rosecrans' Brigade/ Army of Occupation, West Virginia (May- June, 1861)
Army of Occupation (July 23- October 11, 1861)
Department of West Virginia (October 11, 1861- March 11, 1862)
Left Wing, Army of the Mississippi (June 26- October 24, 1862)
District of Corinth (July- October 20, 1862)
Army of the Cumberland (October 30, 1862- October 20, 1863)
Department of Missouri (January 30- December, 1864)