Following his father's career path, Barbour was admitted to the Virginia bar in 1841 and began his legal practice in Culpeper. Five years later he ran for and won election as a member of the Virginia House of Delegates, serving (part-time, along with his private legal practice) from 1847 to 1851. Barbour became president of the Orange and Alexandria Railroad Co., serving from 1852 to 1881.[3]
During the American Civil War, Barbour was a Confederate officer, as was his younger brother James. The family's Fleetwood Hill hosted General J. E. B. Stuart after the Confederate victory at the Battle of Chancellorsville, but the June 1863 engagement with Union forces, the Battle of Brandy Station (perhaps the largest cavalry battle of the war) was considered a draw.
After the war, both John and James resumed their legal careers, but while John concentrated in railroad matters, James bought the Richmond Enquirer and became its editor. After the restoration of civil rights to Confederate officers, John Barbour was elected as a Democrat to the 47th and two succeeding Congresses (March 4, 1881 - March 3, 1887). He succeeded Eppa Hunton II, a fellow Shenandoah Valley lawyer who declined to seek renomination. Barbour served as chairman of the Committee on the District of Columbia (48th and 49th Congresses). He declined to be a candidate for renomination in 1886, months [quantify] after the death of his wife (and the year after his brother James was elected to Virginia's House of Delegates).
In the late 1880s, Barbour joined with other Conservative Democrats and opposed the Readjuster Party, a coalition of blacks and Republicans led by Harrison H. Riddleberger and William Mahone. He helped form the first political machine of "Conservative Democrats", whose power lasted 80 years until the demise of the Byrd Organization in the late 1960s.
In 1888, Barbour ran to succeed Senator Riddleberger when he declined to seek re-election (and died the following year).[citation needed] Elected as a Democrat to the United States Senate Barbour served from March 4, 1889, until his death.[3] Hunton was appointed to serve until the election for the remainder of the term, which he won but declined to seek a full term.
Memorial Services for John S. Barbour Jr. 52nd Cong., 2nd sess., 1892–1893. Washington, D.C.: Government Printing Office, 1893
Quinn, James Thomas. "Senator John S. Barbour, Jr. and the Restoration of Virginia Democracy, 1883-1892." Master's thesis, University of Virginia, 1966.