During this period he studied law and began practice in 1839. After his tenure as adjutant general ended on January 18, 1841, McLeod was commissioned a brigadier general on June 17 and appointed commander of the military component of the Texan Santa Fe expedition by President Mirabeau B. Lamar. McLeod's illness delayed the expedition somewhat and was perhaps a contributing factor in its failure. He was captured with the rest of the expedition and interned at Perote Prison through the summer of 1842. As an important prisoner, he was reported to have been treated well by his Mexican captors. Later that year he married Rebecca Johnson Lamar, a cousin of President Lamar. The couple had two children: a daughter, who died in infancy, and a son. Upon his return to Texas McLeod was appointed to the House of Representatives of the Seventh Congress (1842-43) from Bexar County, to fill the seat Samuel A. Maverick was forced to vacate when he was captured and taken to Mexico by Adrián Woll's raiders in September 1842. In 1844 he was returned to the House, again representing Bexar County, in the Ninth Congress (1844-45). In national politics McLeod was a Democrat except for a brief flirtation with the Know-Nothing party (or American party) in the mid-1850s, but locally he was a member of the anti-Houston faction. Before the Mexican War McLeod was once again appointed adjutant general of Texas.
He subsequently retired from public life and in 1850 became involved in the Buffalo Bayou, Brazos and Colorado Railway, the first railroad company in Texas. In 1855 he was a delegate to the southern commercial convention in New Orleans. McLeod was commissioned a lieutenant colonel of state troops at the time of secession from the Union and participated in the capture of the federal forts on the lower Rio Grande. During the Civil War he was elected lieutenant colonel of the First Texas Infantry Regiment of what was later became Hood's Texas Brigade. When the regimental commander, Louis T. Wigfall, was promoted to brigadier general, McLeod was promoted to colonel and assigned to command of the regiment. He died of pneumonia near Dumfries, Virginia, on January 2, 1862. His body was returned to Texas and is buried in the State Cemetery in Austin. McLeod was characterized as a "fat, jovial man" and said to have been popular, in spite of his violent attacks on Sam Houston.
30° 15.921, -097° 43.645
Texas State Cemetery