While recuperating, he served on the Fitz John Porter court-martial, a highly political case, where his loyalties are believed to have cost him promotion.

At the beginning of the Civil War, Ricketts served in the defenses of Washington, D.C., and commanded an artillery battery in the capture of Confederate-held Alexandria, Virginia, in early 1861.

For his personal bravery in the face of overwhelming odds, on that same day Ricketts was brevetted as a lieutenant colonel in the Regular Army.

At Second Bull Run, his division was thrown forward by McDowell into Thoroughfare Gap to bar the advance of James Longstreet, who was seeking to unite his wing with that of Stonewall Jackson.

The trial was created to convict, with every judge beholden to Edwin M. Stanton for tenure or impending promotion except for Benjamin M. Prentiss.

He did not return to the field until March 1864, when he was assigned to a division of John Sedgwick's VI Corps, which he led through Ulysses S. Grant's Overland Campaign.

The division performed poorly at the Battle of the Wilderness, having one of its brigadiers and several hundred men taken prisoner by the Confederates, and without note at Spotsylvania Court House.

However, Ricketts received the brevet of colonel, Regular Army, for gallant and meritorious services at Cold Harbor, Virginia, June 3, 1864, where he and his men performed well.

At the Battle of Cedar Creek, he commanded the VI Corps in the initial hours of the fighting but was wounded by a Minié ball through his chest that disabled him for life.

Despite his poor health, he returned to command of his division two days before Robert E. Lee's surrender at Appomattox Court House, April 9, 1865.

In late July 1865, Ricketts was assigned to the command of a district in the Department of Virginia, a post he held until April 30, 1866, when he was mustered out of the volunteer service.

[6] Never in good health due to his chest wound suffered while serving in the Shenandoah Valley, after Ricketts retired from the army, he lived in Washington, D.C., for the rest of his life.