Moving to the Western Theater with the IX Corps, Leasure continued in brigade command under Maj. Gen. John Parke during the Siege of Vicksburg and Blue Springs. Returning to command of the 100th Pennsylvania he took part in the Siege of Knoxville. Returning to Virginia, Leasure now commanded the 2nd Brigade, 1st Division in the IX Corps at the Battle of the Wilderness and the Battle of Spotsylvania. When division commander Brig. Gen. Thomas G. Stevenson was killed during the fighting at Spotsylvania, Leasure was the ranking subordinate and took command of the division for 3 days until relieved of this capacity by Maj. Gen. Thomas L. Crittenden. Returning to command the 2nd Brigade, Leasure was wounded a few days later and never returned to field command.