McCandless, nicknamed "Buck", was born in Ireland on September 29, 1834. He was raised by his Uncle after his parents death when he was a young child. The family emigrated to Philadelphia, Pennsylvania when McCandless was six years old. He attended public schools and apprenticed as a machinist at Norris Locomotive Works. He studied law and entered the bar in 1858.[1]
When William Sinclair was wounded in the Battle of Fredericksburg, McCandless succeeded him in command of the 1st Brigade of the Reserves under George Gordon Meade. The division was, at that time, 3rd Division, I Corps. It had penetrated the Confederate right flank along the line of A. P. Hill’s Light Division. After Fredericksburg, the division was transferred to the defenses of Washington, D.C., to recuperate from its losses on active duty.
In May 1863, the Reserves, then commanded by Samuel W. Crawford, returned to the Army of the Potomac and became the 3rd Division of the V Corps. McCandless retained command of the 1st Brigade, and was active in the Battle of Gettysburg. On the second day of the battle, McCandless moved to the army’s left and deployed his men in two lines, together with the 93rd Pennsylvania Infantry of Frank Wheaton’s brigade, at the foot of Little Round Top. McCandless’ brigade, under immediate supervision by Crawford, launched a counterattack against the Confederates, mostly from William T. Wofford’s command, across Plum Run Valley and up slope to the edge of the Wheatfield on July 2, 1863. (Wofford had been ordered to withdraw and did not resist as fiercely as he desired.) McCandless's brigade held its position to the end of the battle. Then it advanced late on July 3, gathering up stragglers from the Confederate withdrawal.[3]
McCandless commanded the division in the Bristoe Campaign in the fall of 1863. He reverted to brigade command and served under Crawford in the Mine Run Campaign. McCandless retained his brigade in the Overland Campaign of Ulysses S. Grant. He was wounded in the Battle of Spotsylvania. Grant and Meade offered him promotion to the rank of brigadier general, but he declined. Colonel McCandless was mustered out of the volunteer service with his regiment on June 6, 1864.
McCandless returned to Philadelphia and resumed his civilian career. He was elected as the first Secretary of Internal Affairs of Pennsylvania in 1874 and served from 1875 until 1879.
He died on June 17, 1884, and was interred at the Mount Moriah Cemetery in Philadelphia, Pennsylvania.[6]