The Thirty-fifth Texas Cavalry (Brown's) organized in October 1863. As there were two units with the number designation of the Thirty-fifth Texas Cavalry, this unit was named after its leader Reuben R. Brown. The other Thirty-fifth Texas Cavalry (Likens's) was led by Col. James B. Likens. When Reuben R. Brown was promoted to colonel, he was placed in charge of a newly-organized battalion that was made of the remnants of his Twelfth Texas Cavalry (Brown's), Rountree's Texas Cavalry, and an assortment of men who wanted to transfer from the Thirteenth Texas Infantry into a mounted unit. The Thirty-fifth was broken down into thirteen companies, some of which shared the geographic origins of its men. For example, Company A, the former core of the Thirteenth Texas Infantry, was known as the "Columbia Blues," since they had formed in Columbia, Texas. Company B was predominately from Brazoria and Colorado counties. Company C men were from Starr and Milam counties. Companies D and F held men from Navarro and Colorado counties. Company G held men from Hardin, Brazoria, and Matagorda counties. Finally Company H held men from Galveston and Fayette counties.
The leader of the unit, Reuben R. Brown, arrived in Texas in 1835 and took part in the ill-fated Matamoros Expedition of 1835–36. In carrying out raids for horses in South Texas, he escaped the battle at Agua Dulce Creek but was captured and brought before Mexican Gen. José Urrea. Eventually, he was taken as one of the Matamoros prisoners and held captive for eleven months before he escaped. Though he initially returned to his home state of North Carolina, he was soon back in Texas, where he owned a plantation in Brazoria County. Early in the Civil War he was assigned the Twelfth Texas Cavalry Battalion.
At the time of its organization, Brown's Thirty-fifth was composed of 927 men, including supporting officers Lt. Col. Stephen William [S. W.] Perkins (often misconstrued as Samuel W. Perkins), and Maj. Lee C. Rountree. The battalion's first duty was to challenge the Federal encampment at Fort Esperanza, located in Matagorda Bay. This fort, which had been recaptured by the Union earlier that year, was a direct threat to Indianola, one of Texas's largest seaports. Although an action was made, on December 29, 1863, the defenses of the fort proved too strong. Through desertion and casualties, Brown found his Thirty-fifth reduced to only twenty-nine officers and 409 men after the affair at Indianola. On February 22, 1864, it fell into the position of sentinel of the coast. Although Brown's Thirty-fifth officially surrendered with the other Trans-Mississippi units at Galveston on June 2, 1865, many of its units had unofficially disbanded in mid-May.