When IX Corps returned to the Army of the Potomac in 1864, Curtin led his regiment at the Battle of the Wilderness in the 2nd Division of Brig. Gen. Robert B. Potter. Curtin took command of 1st Brigade, 2nd Division, on May 11, 1864, after Col. Zenas Bliss was injured at the Battle of Spotsylvania Court House. He led the brigade at the Battle of Cold Harbor and continued in command until June 18, when he was wounded in the Second Battle of Petersburg.