Porter spent his later years as chancellor of his alma mater, the University of Nashville, and as president of Peabody College, which was established at the University of Nashville during his gubernatorial administration. He oversaw the liquidation and transfer of the University of Nashville's assets to the Peabody Education Fund, which allowed Peabody College to be reestablished near Vanderbilt University in 1909.
Porter was born in Paris, Tennessee, the son of Dr. Thomas Kennedy Porter and Geraldine Horton Porter. He attended the University of Nashville, where he obtained a Bachelor of Arts in 1846, and a Master of Arts in 1849. He studied law under Paris attorney John Dunlap (his future father-in-law), and was admitted to the bar in 1851.
Porter was elected to the Tennessee House of Representatives in 1859. In 1861, he introduced the "Porter resolutions," which were eventually adopted. These resolutions stipulated that in the event of war between seceding states and the Union, Tennessee would align itself with the seceding states. In early May 1861, following the Battle of Fort Sumter, these measures were enacted, and Tennessee signed a military pact with the Confederacy.
Porter initially served as an adjutant general under Gideon J. Pillow, and helped organize the Provisional Army of Tennessee. After this army was attached to the greater Confederate Army, Porter was assigned to General Benjamin F. Cheatham. As Cheatham's chief of staff, Porter took part in the battles of Belmont, Shiloh, Chickamauga, Missionary Ridge, and the Siege of Atlanta.
After the war, Porter returned to his law practice in Paris. In 1870, he was a delegate to the state's constitutional convention, which wrote the current Tennessee State Constitution, and served on the convention's judiciary committee. Following the convention, he was elected judge of the state's 12th circuit. Originally a Whig, he aligned himself with the Democratic Party after the Civil War.
Porter received the Democratic nomination for governor in 1874, and easily defeated his Republican opponent, Horace Maynard, by a 105,061 to 55,847 vote later that year. In 1876, he was reelected by a similarly lopsided margin over several candidates, among them moderate Democrat Dorsey B. Thomas and Republican William F. Yardley, the latter being the state's first African-American candidate for governor.
Like his predecessor, John C. Brown, Porter spent much of his gubernatorial tenure managing the state's out-of-control debt. After the state defaulted on its bonded debt in 1875, Porter continued to argue that the state should pay off the bonds in full to protect its credit. The Panic of 1873 had great reduced tax revenues, however, and full repayment proved unfeasible. His successors sought only a partial repayment.
Porter was a strong supporter of public education. While he was governor, the South's first medical school for African Americans, Meharry Medical College, was founded in Nashville. When the Peabody Fund announced it was going to establish a school for teachers in Nashville, Porter used his influence to have the school attached to the University of Nashville. Porter also signed the so-called "Four Mile Law," an early, backdoor form of Prohibition that forbade alcoholic beverages within four miles (6.4 km) of any school. Given the small size of most of the schools of the era and their resultant presence in almost every community, even many of the smallest ones, this effectively outlawed alcohol in all but the least-populated areas of the state.
In his book Appalachian Aspirations, Professor John Benhart describes Porter (and ex-Governor John C. Brown) as "typical of the New South Conservatives who dominated Tennessee politics during the two decades following Reconstruction, mixing the mores of the Old South with a recognition that industrial capitalism was the wave of the future." Following his tenure as governor, Porter remained active in the New South economy. He succeeded Edmund William Cole as the president of the Nashville, Chattanooga and St. Louis Railway from 1880 to 1884, and also served on the Board of Directors of the Tennessee Coal, Iron and Railroad Company.
In 1885, Porter was appointed Assistant Secretary of State by President Grover Cleveland. He served under Secretary of State Thomas F. Bayard. In 1893, during Cleveland's second term, Porter was appointed U.S. Minister to Chile. He remained at this post until the Spring of 1894.
Porter spent the latter part of his life promoting and raising funds for his alma mater, the University of Nashville (from which he had been granted an honorary LL.D. in 1877), and its affiliated Peabody College. He was appointed a trustee of the Peabody Education Fund in 1883, and became president of the Board of Trustees for the University of Nashville in 1890. He became chancellor of the University of Nashville in 1901, and president of Peabody College in 1902. In the latter part of the decade, he oversaw the liquidation of the University of Nashville's assets and their transfer to the Peabody fund for the reestablishment of Peabody College. The fund chose to locate the reorganized college at Vanderbilt's campus, however, leaving Porter embittered. He resigned from the fund's board in 1909.
In 1899, Porter published a book, The Military History of Tennessee, War of 1861-65, which became Volume VIII of Clement Evans's 12-volume series, Confederate Military History. He was also active in the Tennessee Historical Society, at one point serving as its president.
Porter died at his home in Paris in 1912, and is buried in the Paris City Cemetery.
Porter married Susannah Dunlap, the daughter of his law mentor, John Dunlap, in 1851. They had six children, three of whom died at a young age.