King entered politics and was elected as a member of the North Carolina House of Commons, where he served from 1807 to 1809, and he became city solicitor of Wilmington, North Carolina, in 1810.
He was elected to the Twelfth, Thirteenth and Fourteenth Congresses, serving from March 4, 1811, until November 4, 1816, when he resigned to become Secretary of the Legation for William Pinkney during Pinkney's appointment as Minister to Russia and special diplomatic mission in Naples.
He was only 25 years old when he became a congressman for the first time.

When he returned to the United States in 1818, King joined the westward migration of the cotton culture to the Deep South, purchasing property at what would later be known as "King's Bend" between present-day Selma and Cahaba on the Alabama River in Dallas County of the new Alabama Territory, which had been recently separated from Mississippi.
He developed a large cotton plantation based on slave labor, calling the property "Chestnut Hill".
King and his relatives formed one of the largest slaveholding families in the state, collectively owning as many as 500 persons.

William Rufus King was a delegate to the convention which organized the Alabama state government.
Upon the admission of Alabama as the twenty-second state in 1819 he was elected by the State Legislature as a Democratic-Republican to the United States Senate.

King was a follower of Andrew Jackson, and was reelected to the Senate as a Jacksonian in 1822, 1828, 1834, and 1841, serving from December 14, 1819, until his resignation on April 15, 1844.
During this time, in March–April 1824, William R. King was honored with a single vote at the Democratic-Republican Party Caucus to be the party's candidate for the Office of U.S. Vice President for the upcoming 1824 presidential election.
Later he served as President pro tempore of the United States Senate during the 24th through 27th Congresses.
King was Chairman of the Senate's Committee on Public Lands and the Committee on Commerce.

He was appointed as Minister to France, and served from 1844 to 1846.
After his return, King resumed serving in the Senate, appointed and subsequently elected to fill the vacancy caused by the resignation of Arthur P. Bagby.
He held his seat from July 1, 1848, until resigning because of ill health on December 20, 1852, after having been elected vice president.

During the conflicts leading up to the Compromise of 1850, King supported the Senate's gag rule against debate on antislavery petitions and opposed proposals to abolish slavery in the District of Columbia, which was administered by Congress.
King supported a conservative, pro-slavery position, arguing that the Constitution protected the institution of slavery in both the Southern states and the federal territories.
He opposed both the abolitionists' efforts to abolish slavery in the territories as well as the "Fire-Eaters" calls for Southern secession.

On July 11, 1850, two days after the death of President Zachary Taylor, King was appointed Senate President pro tempore.
Because Millard Fillmore ascended to the presidency, the vice presidency was vacant, making King first in the line of succession under the law then in effect.
He also served as Chairman of the Senate's Committee on Foreign Relations and the Committee on Pensions.
King entered politics and was elected as a member of the North Carolina House of Commons, where he served from 1807 to 1809, and he became city solicitor of Wilmington, North Carolina, in 1810. He was elected to the Twelfth, Thirteenth and Fourteenth Congresses, serving from March 4, 1811, until November 4, 1816, when he resigned to become Secretary of the Legation for William Pinkney during Pinkney's appointment as Minister to Russia and special diplomatic mission in Naples. He was only 25 years old when he became a congressman for the first time.
When he returned to the United States in 1818, King joined the westward migration of the cotton culture to the Deep South, purchasing property at what would later be known as "King's Bend" between present-day Selma and Cahaba on the Alabama River in Dallas County of the new Alabama Territory, which had been recently separated from Mississippi. He developed a large cotton plantation based on slave labor, calling the property "Chestnut Hill". King and his relatives formed one of the largest slaveholding families in the state, collectively owning as many as 500 persons.
William Rufus King was a delegate to the convention which organized the Alabama state government. Upon the admission of Alabama as the twenty-second state in 1819 he was elected by the State Legislature as a Democratic-Republican to the United States Senate.
King was a follower of Andrew Jackson, and was reelected to the Senate as a Jacksonian in 1822, 1828, 1834, and 1841, serving from December 14, 1819, until his resignation on April 15, 1844. During this time, in March–April 1824, William R. King was honored with a single vote at the Democratic-Republican Party Caucus to be the party's candidate for the Office of U.S. Vice President for the upcoming 1824 presidential election. Later he served as President pro tempore of the United States Senate during the 24th through 27th Congresses. King was Chairman of the Senate's Committee on Public Lands and the Committee on Commerce.
He was appointed as Minister to France, and served from 1844 to 1846. After his return, King resumed serving in the Senate, appointed and subsequently elected to fill the vacancy caused by the resignation of Arthur P. Bagby. He held his seat from July 1, 1848, until resigning because of ill health on December 20, 1852, after having been elected vice president.
During the conflicts leading up to the Compromise of 1850, King supported the Senate's gag rule against debate on antislavery petitions and opposed proposals to abolish slavery in the District of Columbia, which was administered by Congress. King supported a conservative, pro-slavery position, arguing that the Constitution protected the institution of slavery in both the Southern states and the federal territories. He opposed both the abolitionists' efforts to abolish slavery in the territories as well as the "Fire-Eaters" calls for Southern secession.
On July 11, 1850, two days after the death of President Zachary Taylor, King was appointed Senate President pro tempore. Because Millard Fillmore ascended to the presidency, the vice presidency was vacant, making King first in the line of succession under the law then in effect. He also served as Chairman of the Senate's Committee on Foreign Relations and the Committee on Pensions.
William R. King