John Gregg was born in Lawrence County, Alabama, on September 28, 1828. He studied law after studying at La Grange College, and moved to Fairfield, Texas, in 1852. While in Texas, Gregg was elected in 1856 to be a district judge. In 1861, Gregg was elected to both the secession convention of Texas and to the Provisional Confederate Congress. After the First Battle of Manassas, however, Gregg resigned from the political body and returned to Texas in order to raise troops and fight.
Once back in Texas, Gregg formed the 7th Texas Regiment and was elected to be its colonel. In 1862 Colonel Gregg and the 7th Texas participated in their first battle, the Battle of Fort Donelson. On February 16, Gregg and his unit were captured once the fort surrendered. On August 15, 1862, Gregg was exchanged for Union prisoners, at which time received a promotion to brigadier general. Gregg’s first assignment as brigadier general was to William H. T. Walker’s division in the Western Theatre, where he played significant roles in the battles of Raymond and Jackson. Gregg also participated in the Battle of Chickamauga, where he was severely wounded. Following his recovery, he received assignment to command the Texas Brigade in Robert E. Lee’s Army of Northern Virginia. Gregg participated in many of Lee’s campaigns in the spring of 1864 including the Battle of the Wilderness, the Battle of Cold Harbor, the Battle of Spotsylvania Courthouse, and the Siege of Petersburg. On October 7, 1864, Gregg was killed while leading a counterattack on the Charles City Road near Richmond, Virginia.