In 1828 he became Catholic. In 1830 he married María de Jesús Delgado Curbelo, a descendant of Canary Islanders, and they had six children, whose descendants remained prominent citizens of San Antonio. Between 1827 and 1836 Smith served as military storekeeper, developed mercantile interests, and received a sizable Mexican land grant. He also worked as a civil engineer and surveyor. In December 1835 he escaped the occupying Mexican army of Gen. Martín Perfecto de Cos and joined Gen. Edward Burleson and the Texas army in besieging San Antonio. Smith used his familiarity with the town and his surveying skills to draw the detailed plat that made possible the successful house-to-house attack; he also acted as a guide for one of the assaulting parties. In early 1836 he joined William B. Travis in defense of the Alamo; he was sent by Travis as the final messenger to the Convention of 1836. Subsequently Smith continued as an army scout and participated in the battle of San Jacinto.
After Texas independence was gained, he and his family returned to San Antonio, where Smith became an influential citizen and held a number of offices. He was mayor of San Antonio for three one-year terms during the 1830s and 1840s. He was also alderman, Bexar County tax assessor, clerk of the Bexar County Court, clerk of the Board of Land Commissioners of Bexar County, clerk of the Bexar County Probate Court, treasurer of Bexar County, postmaster of San Antonio, Indian commissioner of the Republic of Texas, and senator from 1842 to January 12, 1845. At one time he held as many as eleven different commissions under presidents Sam Houston and Mirabeau B. Lamar.
The bilingual Smith also began a law practice and formed a real estate company that acted as a middleman between Spanish-speaking owners of land headrights and English-speaking land speculators. He also speculated in land. The combined tax lists of Bexar County for 1842, 1843, and 1844 indicate that he owned eleven town lots and 51,113 acres of undeveloped land, of which 4,428 acres was from his Mexican grant, 320 acres from his bounty grant, and 640 acres from his donation grant. During these years he participated in a real estate partnership with Enoch Jones, which held an additional 41,129 acres. Much of this property was sold to pay Smith's debts and support his family after his death. He died on January 12, 1845, after a brief illness, possibly pneumonia, at Washington-on-the-Brazos and was buried at the site of the current Washington-on-the-Brazos State Historic Site. His remains were later relocated to the Washington City Cemetery, where they are marked by a stone monument.
30° 19.565, -096° 10.167