A Democrat, he was a Unionist and his contemporaries considered him to be a moderate on the issues of sectionalism, slavery, and westward expansion, which contributed to the American Civil War.

[1] He is the only United States vice president to take the oath of office on foreign soil; he was inaugurated in Cuba, due to his poor health.

Admitted to the bar in 1806 after reading the law with Judge William Duffy of Fayetteville, North Carolina, he began practice in Clinton.

He did not reach the constitutional age of 25 for service in the House of Representatives until after the term began, but the Twelfth Congress did not convene until November 4, 1811, and King was not sworn in until then.

After his return, King resumed serving in the Senate and was 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 his resignation on December 20, 1852, because of ill health and his having been elected vice president of the United States.

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 Congress administered.

[2] King supported a pro-slavery position, arguing that the Constitution protected the institution of slavery in both the Southern states and the federal territories.

Andrew Jackson mockingly called them "Miss Nancy" and "Aunt Fancy" (the former being a 19th-century euphemism for an effeminate man[5]), while Representative Aaron V. Brown referred to King as Buchanan's "better half".

[6] However, historian Lewis Saum has pointed out, "Customs and expressions were different in the mid-1800s than they are today... "Miss Nancy" was "a fairly common designation for people who wore clean clothes and had good manners".

Sol Barzman, a biographer of vice presidents, wrote that King's "fastidious habits and conspicuous intimacy with the bachelor Buchanan gave rise to some cruel jibes."

[4] They spent some time apart while King was on overseas missions in France, and their letters remain cryptic and avoid revealing any personal feelings at all.

"[4] Baker concluded that while some of their correspondence was destroyed by family members, the length and intimacy of the surviving letters illustrate "the affection of a special friendship" between King and Buchanan, with no way to know for certain whether it was a romantic relationship.

Because King was ill with tuberculosis and had traveled to Cuba in an effort to regain his health, he was not able to be in Washington to take his oath of office on March 4, 1853.