Robert Bannon Reynolds was born on November 11, 1811, in Knox County, Tennessee, to John and Barbara Reynolds. He grew up and attended school in Tennessee, and he was admitted to the bar in the early 1830s. He served as attorney general for the state’s Second Judicial District from 1839 until 1845.
In 1846, he received a commission as an assistant quartermaster in the United States Army. He took part in the Mexican American War, and he was promoted to paymaster in March 1847. By 1860, he was living in Knox County, and he owned $15,000 of real estate and $8,000 of personal property. He owned at least two enslaved people.
He supported the Confederacy during the Civil War. He resigned from the United States Army on June 23, 1861. According to an early biographer, he received a commission as a paymaster in the Confederate army, but he declined the appointment.
After the war, he spent several years in Virginia, Illinois, and Missouri, before returning to Knox County. He earned a living as a lawyer. He married Mary Kennedy on May 6, 1875, and they had at least two children: Mary, born around 1877; and Robert, born around 1879. He died in Knoxville, Tennessee, on December 3, 1896.