He unsuccessfully ran for
Congress in 1843.
In 1844 he was a presidential elector, and cast his ballot for
James K. Polk and
George M. Dallas. He ran unsuccessfully for governor in 1847, and lost the Democratic nomination to
George W. Towns; Towns won the general election, and in 1848 he appointed Johnson to the
United States Senate seat vacated by the resignation of
Walter T. Colquitt. Johnson served from February 4, 1848, to March 3, 1849, but was not a candidate for election to the seat. He returned to Georgia and served as a circuit court judge from 1849 to 1853. Johnson was a
presidential elector in
1852. In 1850, Johnson was a pro-slavery politician with strong secessionist leanings. In
1853, he was elected governor of Georgia, then re-elected in
1855. During the
1856 presidential campaign, Johnson declared that a
Frémont victory would be grounds for secession. But while serving as governor, Johnson switched positions and became a strong unionist. After he finished his term as governor in 1857,
Johnson County, Georgia was named in his honor. In 1860, when the Democratic Party refused to add the support of extending slavery to the western territories to its platform, the party split. To try to recapture some southern votes, Johnson was chosen as the northern Democrats' nominee as the running mate of presidential candidate
Stephen A. Douglas. He was also a slave owner. In 1840, he owned 34 slaves in Jefferson County, Georgia. In 1850, he owned 7 slaves in Milledgeville, Georgia. He also owned 60 additional slaves in Jefferson County, Georgia. In 1860, he owned 115 slaves in Jefferson County, Georgia. ==Civil War==