The 1862–63 United States Senate elections were held on various dates in various states, occurring during the American Civil War. As these U.S. Senate elections were prior to the ratification of the Seventeenth Amendment in 1913, senators were chosen by state legislatures. Senators were elected over a wide range of time throughout 1862 and 1863, and a seat may have been filled months late or remained vacant due to legislative deadlock. In these elections, terms were up for the senators in Class 1.

The Unionist Party, later known as the Unconditional Union Party in the border states, was a political party in the United States started after the Compromise of 1850 to define politicians who supported the Compromise. It was used primarily as a label by politicians who did not want to affiliate with the Republicans, or wished to win over anti-secession Democrats. Members included Southern Democrats who were loyal to the Union as well as elements of the old Whig Party and other factions opposed to a separate Southern Confederacy.