Juan Seguín, political and military figure of the Texas Revolution and Republic of Texas, was born in San Antonio on October 27, 1806, the elder of two sons of Juan José María Erasmo Seguín and María Josefa Becerra. Although he had little formal schooling, Juan was encouraged by his father to read and write, and he appears to have taken some interest in music. At age nineteen he married María Gertrudis Flores de Abrego, a member of one of San Antonio's most important ranching families. They had ten children, among whom Santiago was a mayor of Nuevo Laredo and Juan, Jr., was an officer in the Mexican military in the 1860s and 1870s. Seguín began his long career of public service at an early age. He helped his mother run his father's post office while the latter served in Congress in 1823–24. Seguín's election as alderman in December 1828 demonstrated his great potential. He subsequently served on various electoral boards before being elected alcalde in December 1833. He acted for most of 1834 as political chief of the Department of Bexar, after the previous chief became ill and retired.
Seguín's military career began in 1835. In the spring he responded to the Federalist state governor's call for support against the Centralist opposition by leading a militia company to Monclova. After the battle of Gonzales in October 1835, Stephen F. Austin granted a captain's commission to Seguín, who raised a company of thirty-seven. His company was involved in the fall of 1835 in scouting and supply operations for the revolutionary army, and on December 5 it participated in the assault on Gen. Martín Perfecto de Cos's army at San Antonio. Seguín entered the Alamo with the other Texan military when Antonio López de Santa Anna's army arrived, but was sent out as a courier. Upon reaching Gonzales he organized a company that functioned as the rear guard of Sam Houston's army, was the only Tejano unit to fight at the battle of San Jacinto, and afterward observed the Mexican army's retreat. Seguín accepted the Mexican surrender of San Antonio on June 4, 1836, and served as the city's military commander through the fall of 1837; during this time he directed burial services for the remains of the Alamo dead. He resigned his commission upon election to the Texas Senate at the end of the year.
Seguín, the only Mexican Texan in the Senate of the republic, served in the Second, Third, and Fourth Congress. He served on the Committee of Claims and Accounts and, despite his lack of English, was chairman of the Committee on Military Affairs. Among his legislative initiatives were efforts to have the laws of the new republic printed in Spanish. In the spring of 1840 he resigned his Senate seat to assist Gen. Antonio Canales, a Federalist, in an abortive campaign against the Centralists, but upon his return to San Antonio at the end of the year he found himself selected mayor. In this office Seguín became embroiled in growing hostilities between Anglos and Mexican Texans. He faced personal problems as well. He had gained the enmity of some residents by speculating in land. He financed his expedition in support of Canales by mortgaging property and undertook a smuggling venture in order to pay off the debt. Although upon his return from Mexico he came under suspicion of having betrayed the failed Texan Santa Fe expedition, he still managed to be reelected mayor at the end of 1841. His continuing conflicts with Anglo squatters on city property, combined with his business correspondence with Mexico, incriminated him in Gen. Rafael Vásquez's invasion of San Antonio in March 1842. In fear for his safety, Seguín resigned as mayor on April 18, 1842, and shortly thereafter fled to Mexico with his family.
He spent six years in Mexico and then attempted to reestablish himself in Texas. While living in Mexico he participated, according to him under duress, in Gen. Adrián Woll's invasion of Texas in September 1842. Afterward his company served as a frontier defense unit, protecting the Rio Grande crossings and fighting Indians. During the Mexican War his company saw action against United States forces. At the end of the war he decided to return to Texas despite the consequences. He settled on land adjacent to his father's ranch in what is now Wilson County. During the 1850s he became involved in local politics and served as a Bexar County constable and an election-precinct chairman. His business dealings took him back to Mexico on occasion, and at the end of the 1860s, after a brief tenure as Wilson county judge, Seguín retired to Nuevo Laredo, where his son Santiago had established himself. He died there on August 27, 1890. His remains were returned to Texas in 1974 and buried at Seguin, the town named in his honor, during ceremonies on July 4, 1976.