Holt joined the
Army as a colonel in 1862 and was appointed by President Abraham Lincoln to be the
Judge Advocate General of the
Union Army. As Judge Advocate General of the Army, Holt oversaw the expansion of military law to include the military prosecutions of citizens who were not in the military service. He crafted the argument to the Supreme Court in Ex Parte Vallandigham, By the time he joined the Army, he believed that the only means to prevent treason from occurring again was to ensure that slavery was abolished for all time, and eventually equal treatment under the law enforced in the South. In 1864, he was promoted to brigadier general. He was the first Judge Advocate General to hold a general's rank. He personally prosecuted the court-martial against Major General
Fitz John Porter for crimes of
disobedience of a lawful order and misbehavior in front of the enemy. Lincoln also offered Holt the position of
Secretary of the Interior that same year and
Attorney General later in 1864, but Holt declined both offices. For instance, Holt crafted legislation that stripped Union Army deserters of their citizenship. The Supreme Court overturned this legislation in Tropp v. Dulles in 1958. Holt's reasoning for this law was that Copperheads and other pro-slavery southern sympathizers encouraged desertions. Holt also used the Army's power to suppress newspapers as well as oversee the arrest and trial of Congressman
Benjamin Gwinn Harris of Maryland who "uttered treasonous statements" in the House of Representatives. They were executed on July 7, 1865, making Surratt the first woman to be executed by the U.S. federal government. Holt's public image was damaged by the trial and his prosecution of it, and many historians believe that the controversy surrounding it ended Holt's political career. In 1866, Holt issued a pamphlet, titled
Vindication of Judge Advocate General Holt From the Foul Slanders of Traitors, Confessed Perjurers and Suborners, Acting in the Interest of Jefferson Davis, in which he attempted to defend himself against the various allegations and clear up some of the confusion stemming from the trial. ==Later life==