Using antislavery counsel, Scott petitioned his Missouri owner for freedom in 1846; he served her late husband in free territory. A state court freed him in 1850, but Missouri's Supreme Court overruled it.

Scott sued his new owner, John Sandford, in Federal Court as a citizen of Missouri (1854). But the Court ruled that he was a slave and could not sue. On appeal, the Supreme Court concurred. It declared the Missouri Compromise unconstitutional, that blacks were not citizens, and “had no rights that the white man was bound to respect.” Abolitionists decried its decision, which exacerbated North–South conflict over slavery.