He assumed the presidency following the assassination of Abraham Lincoln, as he was vice president at that time. Johnson was a Democrat who ran with Lincoln on the National Union Party ticket, coming to office as the Civil War concluded. He favored quick restoration of the seceded states to the Union without protection for the newly freed people who were formerly enslaved. This led to conflict with the Republican-dominated Congress, culminating in his impeachment by the House of Representatives in 1868. He was acquitted in the Senate by one vote.
Johnson was born into poverty and never attended school. He was apprenticed as a tailor and worked in several frontier towns before settling in Greeneville, Tennessee. He served as alderman and mayor there before being elected to the Tennessee House of Representatives in 1835. After briefly serving in the Tennessee Senate, Johnson was elected to the House of Representatives in 1843, where he served five two-year terms. He became governor of Tennessee for four years, and was elected by the legislature to the Senate in 1857. During his congressional service, he sought passage of the Homestead Bill which was enacted soon after he left his Senate seat in 1862. 