[53] Harrison finally returned to his old regiment the same day that news of President Lincoln’s assassination was received.[48] He rode in the Grand Review in Washington, D.C. before mustering out with the 70th Indiana on June 8, 1865.[38][48]

Post-war career
Indiana politics
While serving in the Union Army in October 1864, Harrison was once again elected reporter of the Indiana Supreme Court, although he did not seek the position, and served as the Court's reporter for four more years. The position was not a politically powerful one, but it provided Harrison with a steady income for his work preparing and publishing court opinions, which he sold to the legal profession.[54][55] Harrison also resumed his law practice in Indianapolis. He became a skilled orator and known as "one of the state's leading lawyers".[24]
In 1869 President Ulysses S. Grant appointed Harrison to represent the federal government in a civil suit filed by Lambdin P. Milligan, whose controversial wartime conviction for treason in 1864 led to the landmark U.S. Supreme Court case Ex parte Milligan.[56][57] The civil case was referred to the U.S. Circuit Court for Indiana at Indianapolis, where it evolved into Milligan v. Hovey.