The Union defeat at Bull Run in July 1861, followed by the death of Senator Edward D. Baker at the Battle of Ball's Bluff in October, prompted elected officials to call for an inquiry into the dramatic losses. "We see many things done which do not meet the public approbation,” Maine senator William Pitt Fessenden declared. “We see some things done which we do not approve ourselves, and which evidently call for an investigation, or, at any rate, call for such an explanation as shall satisfy the people."

The concurrent resolution, passed on December 10, 1861, created a joint committee comprised of three senators and four representatives and granted its members the power to "inquire into the conduct of the present war and to send for persons and papers." The Joint Committee on the Conduct of the War pursued a broad investigatory agenda that included failed military campaigns, corruption in military supply contracts, the mistreatment of Union prisoners by Confederate forces, the massacre of Cheyenne Indians, Union trade activities, and gunboat construction. The joint committee continued its work into 1865, meeting 272 times over four years and producing copious reports based on its field work and the testimony of dozens of witnesses.