Significance: Associate Justice Nelson participated in important Supreme Court cases dealing with slavery and the Civil War.
Nelson began practicing law in 1817. He served as a state judge in New York from 1823 to 1831, when he was appointed to the state supreme court. He was nominated to the Supreme Court by President John Tyler in 1845 and quickly approved by the Senate. Nelson was an authority on international law, maritime law, and patent law. He wrote hundreds of opinions for the Court, often dealing with technical aspects. His opinion in Scott v. Sandford (1857) avoided the controversial issue of whether the federal government could forbid slavery in new territories. This opinion, originally intended to be the majority opinion of the Court, was replaced by a stronger opinion written by Chief Justice Roger Brooke Taney that denied the federal government this power. In the Prize Cases (1863), involving a blockade of Confederate ports ordered by President Abraham Lincoln during the Civil War (1861-1865), Nelson dissented from the majority by declaring that only Congress, not the president, could declare war. In Ex parte Milligan (1866), Nelson agreed with the majority in reversing a military commission's decision to hang a civilian convicted of treason, declaring that a jury trial was necessary.