John Tyler's tenure as the tenth president of the United States began on April 4, 1841, after the death of President William Henry Harrison, and ended on March 4, 1845. He had been Vice President of the United States for only days when he assumed the presidency. Tyler was the first to succeed to the office without being elected to it. To forestall constitutional uncertainty, Tyler took the presidential oath of office on April 6. He then moved into the White House, assumed full presidential powers, and served out the balance of Harrison's four-year term, setting the Tyler Precedent that would govern future extraordinary successions and eventually become codified in the Twenty-fifth Amendment. He was succeeded by James K. Polk of the Democratic Party.

Although nominated for the vice presidency on the Whig Party ticket in 1840, Tyler did not share the views held by some members of his party on various issues. That did not, however, become a problem until after the 1840 election, because during that campaign, the party had not taken clear stands on specific issues such as a national bank and protective tariff. Instead, it had emphasized attacking incumbent Democratic President Martin Van Buren and proclaiming colorful slogans about log cabins and hard cider. After the election, however, as a strict constructionist, Tyler found some of the program then introduced by the Whigs in Congress unconstitutional and thus vetoed several bills favored by party leader Henry Clay. Among the bills vetoed by Tyler was a measure to re-establish a national bank. In response to these vetoes, most of Tyler's cabinet resigned, and Whig congressmen expelled Tyler from the party. A resolution calling for his impeachment was introduced in the House, though it was later defeated. Despite his disagreements with Congress, Tyler did sign the Tariff of 1842, which provided needed revenue to a government still dealing with the effects of the Panic of 1837.

Tyler had more success in international affairs. His administration negotiated the Webster–Ashburton Treaty, which settled a contentious territorial dispute with the United Kingdom. Tyler also emphasized American interests in the Pacific Ocean, and he reached a commercial treaty with Qing China, known as the Treaty of Whangia. He also extended the principles of the Monroe Doctrine to Hawaii, in a policy that became known as the "Tyler Doctrine." During his last two years in office Tyler pressed for the annexation of Texas, thereby introducing the annexation issue into the 1844 presidential election, and initially ran for a full term, under the banner of the Tyler Party. Because of his injection of that issue, pro-annexation Democrats blocked the renomination of former President Van Buren, who opposed annexation and nominated instead the previously little known James K. Polk. After Tyler withdrew from the race, he endorsed Polk for the presidency. Polk went on to defeat Clay, the Whig candidate, in the general election. On March 1, 1845, three days before turning the presidency over to Polk, Tyler signed a Texas annexation bill into law, and Texas would be admitted as a state in the first year of Polk's presidency.

Tyler's presidency has provoked highly divided responses, but he is generally held in low esteem by historians. Edward P. Crapol began his biography John Tyler, the Accidental President (2006) by noting: "Other biographers and historians have argued that John Tyler was a hapless and inept chief executive whose presidency was seriously flawed."Crapol, pp. 2–3. In The Republican Vision of John Tyler (2003), Dan Monroe observed that the Tyler presidency "is generally ranked as one of the least successful".Monroe, p. 3. But both of those authors used those statements as a preface to their presenting a more balanced view of Tyler's presidency. Some historians and commentators have praised Tyler's foreign policy, personal conduct, and the precedent he set with regards to presidential succession.

Accession

In the 1840 presidential election, the Whig ticket of William Henry Harrison and John Tyler defeated the Democratic ticket led by incumbent President Martin Van Buren. Tyler was sworn in as the nation's 10th vice president on March 4, 1841. Following Harrison's two-hour speech on a cold and overcast March 4, the vice president returned to the Senate to receive the president's cabinet nominations, presiding over the confirmations the following day. Expecting few responsibilities, he then left Washington for his home in Williamsburg.Chitwood, pp. 200–02.Seager, pp. 144–45. After his inauguration, Harrison called for a special session of Congress, to begin in late May, in order to address the dangerous financial condition of a country still in the midst of the Panic of 1837.Peterson, pp. 38–39. The first few weeks of the presidency took a toll on Harrison's health, and after being caught in a rainstorm in late March he came down with pneumonia and pleurisy. Harrison's old age and fading health were no secret during the campaign, and the question of the presidential succession was on every politician's mind.Chitwood, pp. 201–02.Seager, pp. 142–47.

Secretary of State Daniel Webster sent word to Tyler of Harrison's illness on April 1,Crapol, p. 8. and on April 5, Tyler learned that Harrison had died on the preceding day. Harrison's death while in office was an unprecedented event that caused considerable uncertainty regarding presidential succession. Legal scholars had long anticipated that a president would die in office at some point, but no firm consensus existed as to whether or not the vice president would fully assume the office of the presidency.Peterson, pp. 47–48. Article II, Section 1, Clause 6 of the United States Constitution, which governed intra-term presidential succession at the timeThis constitutional provision was later superseded by the Twenty-fifth Amendment states that:

The text of this Constitutional prescription led to the question of whether the actual office of president, or merely the president's powers and duties, devolved upon Vice President Tyler. The cabinet met within an hour of Harrison's death and, according to a later account, determined that Tyler would be "vice-president acting President".Dinnerstein, p. 447. But Tyler firmly and decisively asserted that the Constitution gave him the full and unqualified powers of the office. Accordingly, he had himself sworn in immediately as president, moved into the White House and assumed full presidential powers. This set the critical Tyler Precedent for an orderly transfer of power following a president's death, though it was not codified until the passage of the 25th Amendment in 1967. The presidential oath was administered by Chief Judge William Cranch of the U.S. Circuit Court of the District of Columbia in Tyler's hotel room. Tyler had initially questioned the necessity of taking the oath, arguing that it was redundant to his oath as vice president, but agreed to it in order to quell any doubt over his accession.Chitwood, pp. 202–03.

Tyler delivered an inaugural address before Congress on April 9, in which he reasserted his belief in fundamental tenets of Jeffersonian democracy and limited federal power. Tyler's claim to be president was resisted by many members of Congress. Representative (and former president) John Quincy Adams felt that Tyler should be a caretaker under the title of "acting president", or remain vice president in name.Chitwood, pp. 203–07. Also among those who questioned Tyler's authority was Senator Henry Clay, who had planned to be "the real power behind a fumbling throne" while Harrison was alive, and intended the same for Tyler. Clay saw Tyler as the "vice-president" and his presidency as a mere "regency".Seager, pp. 142, 151.

After some heated debate, Congress confirmed Tyler's interpretation that he was, indeed, the new president. In both houses, unsuccessful amendments were offered to strike the word "president" in favor of language including the term "vice president" to refer to Tyler. Mississippi Senator Robert J. Walker, in opposition, stated that the idea that Tyler was still vice president and could preside over the Senate was absurd.Dinnerstein, pp. 451–53. Tyler never wavered from his conviction that he was the rightful president; when his political opponents sent correspondence to the White House addressed to the "vice president" or "acting president", Tyler had it returned unopened.Crapol, p. 10.

Administration

Fearing that he would alienate Harrison's supporters, Tyler decided to keep the dead president's entire cabinet even though several members were openly hostile to him and resented his assumption of the office. At his first cabinet meeting, Tyler was informed that Harrison had let major policy decisions be resolved by a majority vote, and that the cabinet expected the new president to continue this practice. Tyler was astounded and immediately corrected them:

With the exception of Secretary of State Webster,Peterson, pp. 146–147. the new president had no allies in the cabinet, and moreover soon discovered that he had few in Congress either. Adhering to his states' rights, strict-constructionist ideology and having joined the Whigs only in opposition to Andrew Jackson, he did not embrace the American System of internal improvements, protective tariffs, and national bank proposals of the party leaders. Following Tyler's veto of two Whig banking bills, in September 1841 all the members of the cabinet except Webster resigned in protest, a maneuver that Clay had engineered. Having suspected that much of the cabinet would resign, Tyler quickly put together a new cabinet consisting of Whigs opposed to Clay.May, pp. 75–76

Webster had long struggled with his role in the Whig Party and the Tyler administration, and he finally resigned from the cabinet in May 1843.Peterson, pp. 167–169, 180. Abel Upshur replaced Webster as Secretary of State, and he focused on Tyler's priority of annexing the Republic of Texas. In hopes of building up his own party of Southern Whigs and Northern Democrats, the Tyler administration removed several other important officials in favor of "Tyler Men." One of these supposed loyalists, Thomas Gilmer, replaced Upshur as Secretary of the Navy.May, pp. 99–101. The shakeup left Tyler's cabinet composed equally of Democrats and Whigs.Peterson, p. 183. Many of Tyler's later appointments, including Upshur and Gilmer, were followers of Senator John C. Calhoun of South Carolina; unknown to Tyler, their actions were calculated to boost Calhoun's 1844 presidential candidacy.Peterson, p. 187. After Upshur and Gilmer were both killed in a naval accident in early 1844, Tyler brought in Calhoun as Secretary of State and John Y. Mason of Virginia as Secretary of the Navy.Peterson, pp. 203–204, 210. Later that year, Secretary of the Treasury John C. Spencer left the cabinet and was replaced by George M. Bibb, leaving Tyler's cabinet with just one Northerner, Secretary of War William Wilkins.Peterson, p. 231.

Tyler was the first president to have his cabinet nominees rejected by the Senate. The four rejected nominees were Caleb Cushing (Treasury), David Henshaw (Navy), James Porter (War), and James S. Green (Treasury). Henshaw and Porter served as recess appointees before their rejections. Tyler repeatedly renominated Cushing, who was rejected three times in one day, March 3, 1843, the last full day of the 27th Congress. After the end of Tyler's term, a cabinet nominee would not again be rejected by the Senate until the 1860s.