Polk was the oldest of ten children born in a farmhouse in what is now Pineville, North Carolina in Mecklenburg County on November 2, 1795, just outside Charlotte. His father, Samuel Polk, was a slaveholder, successful farmer and surveyor of Scots-Irish descent. Polk grew up in an environment where slavery was a normal accepted practice and there is no suggestion that he ever saw it as an evil.
Polk served as Speaker of the House of Representatives from 1835 to 1839. The two major issues during Polk's term as speaker were slavery and the economy. During his term, Polk issued the gag rule on petitions from abolitionists, one which was often challenged and tested by Massachusetts Congressman (and former President) John Quincy Adams.
Slavery was a major issue in the election of 1844, more specifically, US expansion and whether or not new territory would allow slavery. The leading contender for the presidential nomination was former President Martin Van Buren, who wanted to stop the expansion of slavery. The main point of political contention involved the Republic of Texas, which, after declaring independence from Mexico in 1836, had asked to join the United States. Van Buren opposed the annexation but in doing so lost the support of many Democrats, including former President Andrew Jackson. At the Democratic nominating convention that year, Van Buren won a simple majority on the convention's first ballot but did not attain the two-thirds majority needed for the nomination. When it became clear after another six ballots that Van Buren would not win the required majority, Polk emerged as a "dark horse" candidate and an indecisive eighth ballot, the convention unanimously nominated Polk.
During his presidency, many abolitionists criticized Polk as an instrument of slave owners, and claimed that spreading slavery was the reason he supported annexing Texas and later war with Mexico. Polk wrote in his diary that he believed slavery could not exist in the territories won from Mexico, but refused to endorse the Wilmot Proviso that would forbid it there. Polk argued instead for extending the Missouri Compromise line to the Pacific Ocean, which would prohibit the expansion of slavery above 36° 30' west of Missouri, but allow it below that line if approved by eligible voters in the territory. In Slavemaster President, William Dusinberre argues that Polk's diary, which he kept during his presidency, was written for later publication, and does not represent Polk's policy at the time.
Polk was a slaveholder for his entire life. His father had left Polk more than 8,000 acres of land, and divided about 53 slaves to his widow and children after he died. James inherited twenty of his father's slaves, either directly or from deceased brothers. In 1831, he became an absentee cotton planter, sending slaves to clear plantation land that his father had left him near Somerville, Tennessee. Four years later Polk sold his Somerville plantation and, together with his brother-in-law, bought 920 acres of land, a cotton plantation near Coffeeville, Mississippi. He ran this plantation for the rest of his life, eventually taking it over completely from his brother-in-law.
Polk rarely sold slaves, although once he became President and could better afford it, he bought more. Polk's will stipulated that their slaves were to be freed after his wife Sarah had died. However, the 1863 Emancipation Proclamation and the 1865 Thirteenth Amendment to the United States Constitution freed all remaining slaves in rebel states long before the death of his wife in 1891.
William Dusinberre argues that, unlike many antebellum planters who portrayed their involvement with slavery as a historical burden thrust upon them by their ancestors, Polk entered the slave business of his own volition, for reasons principally of financial self-interest. Critics have described Dusinberre's book as "the most careful and vivid account to date of how slavery functioned on a single cotton plantation." One summary of the book states:
" Life at the Polk estate was brutal and often short. Fewer than one in two slave children lived to the age of fifteen, a child mortality rate even higher than that on the average plantation. A steady stream of slaves temporarily fled the plantation throughout Polk's tenure as absentee slavemaster. Yet Polk was in some respects an enlightened owner, instituting an unusual incentive plan for his slaves and granting extensive privileges to his most favored slave. Startlingly, Dusinberre shows how Polk sought to hide from public knowledge the fact that, while he was president, he was secretly buying as many slaves as his plantation revenues permitted...Dusinberre suggests that the president's political stance toward slavery-- influenced as it was by his deep personal involvement in the plantation system-- may actually have helped precipitate the Civil War that Polk sought to avoid."