The Twenty-fifth Texas Cavalry, also known as the Third Texas Lancers, was organized from part of the Twenty-first Texas Cavalry on April 24, 1862, at Hempstead, Texas. It was organized and commanded by Col. Clayton C. Gillespie with field officers Maj. Joseph N. Dark, Maj. Edward B. Pickett, and Lt. Col. William M. Neyland. The regiment comprised eight companies lettered A to H with men from the Texas counties of Angelina, Goliad, Hardin, Hunt, Jasper, Liberty, Rusk, Trinity, Tyler, and Walker. The regiment was on duty in Texas as a dismounted unit from its inception to August 1862.
On August 5, 1862, the regiment was transferred to the District of Arkansas. While there the regiment saw some action near Fayetteville on October 27–28, 1862, and took part in the battle of Arkansas Post on January 10–11, 1863. The men of the Twenty-fifth Texas Cavalry were taken prisoner after the Union victory at Arkansas Post with most of them being held at Camp Douglas in Illinois through the summer of 1863. They were eventually exchanged, returned to service, dismounted, and consolidated with the Seventeenth, Eighteenth, and Twenty-fourth Texas Cavalry regiments to serve in the Army of Tennessee.
The Twenty-fifth Texas Cavalry was involved in some thirty-seven different actions and engagements and remained in the Army of Tennessee to war's end. Its most notable engagements and campaigns in addition to Arkansas Post were Chickamauga on September 19–20, 1863; the siege of Chattanooga from September to November 1863; the Atlanta campaign from May to September 1864; Jonesboro from August 31 to September 1, 1864; Franklin on November 30, 1864; Nashville on December 15–16, 1864; the Carolinas campaign from February to April 1864; and Bentonville on March 19–21, 1865. Only a small remnant of the Twenty-fifth Texas Cavalry continued under arms when the regiment surrendered on April 25, 1865, in North Carolina. The regiment was officially surrendered by Gen. E. Kirby Smith, commander of the Trans-Mississippi Department, on May 26, 1865.