The Battle of San Jacinto (Spanish: Batalla de San Jacinto), fought on April 21, 1836, in present-day La Porte and Deer Park, Texas, was the final and decisive battle of the Texas Revolution. Led by General Sam Houston, the Texan Army engaged and defeated General Antonio López de Santa Anna's Mexican army in a fight that lasted just 18 minutes. A detailed, first-hand account of the battle was written by General Houston from the headquarters of the Texan Army in San Jacinto on April 25, 1836. Numerous secondary analyses and interpretations have followed.

General Santa Anna, the president of Mexico, and General Martín Perfecto de Cos both escaped during the battle. Santa Anna was captured the next day on April 22 and Cos on April 24. After being held for about three weeks as a prisoner of war, Santa Anna signed the peace treaty that dictated that the Mexican army leave the region, paving the way for the Republic of Texas to become an independent country. These treaties did not necessarily recognize Texas as a sovereign nation but stipulated that Santa Anna was to lobby for such recognition in Mexico City. Sam Houston became a national celebrity, and the Texans' rallying cries from events of the war, "Remember the Alamo" and "Remember Goliad", became etched into Texan history and legend.

General Antonio López de Santa Anna was a proponent of governmental federalism when he helped oust Mexican President Anastasio Bustamante in December 1832. Upon his election as president in April 1833, Santa Anna switched his political ideology and began implementing centralist policies that increased the authoritarian powers of his office. His abrogation of the Constitution of 1824, correlating with his abolishing local-level authority over Mexico's state of Coahuila y Tejas (Coahuila and Texas), became a flashpoint in the growing tensions between the central government and its Tejano and Anglo citizens in Texas. While in Mexico City awaiting a meeting with Santa Anna, Texian empresario Stephen F. Austin wrote to the ayuntamiento (city council) of Béxar (now San Antonio) urging a break-away state. In response, the Mexican government kept him imprisoned for most of 1834.

Colonel Juan Almonte was appointed director of colonization in Texas, ostensibly to ease relations with the colonists and mitigate their anxieties about Austin's imprisonment. He delivered promises of self-governance and conveyed regrets that the Mexican Congress deemed it constitutionally impossible for Texas to be a separate state. Behind the rhetoric, his covert mission was to identify the local power brokers, obstruct any plans for rebellion, and supply the Mexican government with data that would be of use in a military conflict. For nine months in 1834, under the guise of serving as a government liaison, Almonte traveled through Texas and compiled an all-encompassing intelligence report on the population and its environs, including an assessment of their resources and defense capabilities.

In consolidating his power base, Santa Anna installed General Martín Perfecto de Cos as the governing military authority over Texas in 1835. Cos established headquarters in San Antonio on October 9, triggering what became known as the Siege of Béxar. After two months of trying to repel the Texian forces, Cos raised a white flag on December 9 and signed surrender terms two days later. The surrender of Cos effectively removed the occupying Mexican army from Texas. Many believed the war was over, and volunteers began returning home.

In compliance with orders from Santa Anna, Mexico's Minister of War José María Tornel issued his December 30 "Circular No. 5", often referred to as the Tornel Decree, aimed at dealing with United States intervention in the uprising in Texas. It declared that foreigners who entered Mexico for the purpose of joining the rebellion were to be treated as "pirates", to be put to death if captured. In adding "since they are not subjects of any nation at war with the republic nor do they militate under any recognized flag," Tornel avoided declaring war on the United States.

The Mexican Army of Operations numbered 6,019 soldiers and was spread out over 300 miles (480 km) on its march to Béxar. General Joaquín Ramírez y Sesma was put in command of the Vanguard of the Advance that crossed into Texas. Santa Anna and his aide-de-camp Almonte forded the Rio Grande at Guerrero, Coahuila on February 16, 1836, with General José de Urrea and 500 more troops following the next day at Matamoros. Béxar was captured on February 23, and when the assault commenced, attempts at negotiation for surrender were initiated from inside the fortress. William B. Travis, the garrison commander, sent Albert Martin to request a meeting with Almonte, who replied that he did not have the authority to speak for Santa Anna. Colonel James Bowie dispatched Green B. Jameson with a letter, translated into Spanish by Juan Seguín, requesting a meeting with Santa Anna, who immediately refused. Santa Anna did, however, extend an offer of amnesty to Tejanos inside the fortress. Alamo non-combatant survivor Enrique Esparza said that most Tejanos left when Bowie advised them to take the offer.

Cos, in violation of his surrender terms, forded into Texas at Guerrero on February 26 to join with the main army at Béxar. Urrea proceeded to secure the Gulf Coast and was victorious in two skirmishes with Texian detachments serving under Colonel James Fannin at Goliad. On February 27 a foraging detachment under Frank W. Johnson at San Patricio was attacked by Urrea. Sixteen were killed and twenty-one taken prisoner, but Johnson and four others escaped. Urrea sent a company in search of James Grant and Plácido Benavides who were leading a company of Anglos and Tejanos towards an invasion of Matamoros. The Mexicans ambushed a group of Texians, killing Grant and most of the company. Benavides and 4 others escaped, and 6 were taken prisoner.