Reuben Reid Gaines, lawyer and state Supreme Court justice, was born on October 30, 1836, in Sumter County, Alabama, the son of Joab and Lucinda (McDavid) Gaines. His father was a large slaveholder, and he had above-average educational opportunities. He earned a bachelor's degree from the University of Alabama in 1855, studied law briefly at William and Mary College, and graduated from Cumberland University in Lebanon, Tennessee, with a law degree in 1857. He practiced law in Alabama from 1858 to 1861. On March 30, 1859, he married Louisa Shortridge at Montevallo, Alabama, and they had one daughter, born in 1873.
Gaines entered the Confederate Army soon after the outbreak of the Civil War and served with Alabama units throughout the war. He surrendered as part of Gen. Joseph E. Johnston's army in May 1865. In 1866 he and his wife moved to Clarksville, Texas, where he entered law practice with Benjamin H. Epperson and became active in the Democratic party, which he served as a member of the platform committee at the state convention in 1873. At the first elections held under the Constitution of 1876, Gaines was elected district judge of the Sixth Judicial District, in North Texas. He served on the bench until 1884, when he retired to practice law in Paris, Texas.
In November 1886 Governor John Ireland appointed him to an unexpired term as associate justice of the Texas Supreme Court. He won election as a Democrat to the court for a regular six-year term in 1888 and was reelected in 1894. At the death of John W. Stayton in 1894, Gaines was appointed chief justice. He was reelected in 1900 and 1906 and so held the position until 1911. During his long tenure on the court he wrote hundreds of opinions affecting Texas during the years of transition from nineteenth-century agrarian conditions to the much more complex social and economic life of the twentieth century. He became noted for avoiding partisan politics and was said never to have made a political speech on behalf of himself or anyone else.
Gaines retired from the court on January 5, 1911, in poor health. He lived at the Driskill Hotel in Austin until his death, from complications following a stroke, on October 13, 1914. His wife and daughter survived him.