Joseph Johnson was born in Brewerton, Laurens County, the son of Benjamin and Mary Medlock Johnson. He was orphaned at the age of fourteen. He was educated at Erskine College where, in 1897, he was valedictorian when he received his A.B. He received an honorary LL.D. in 1916. He studied law at the Vanderbilt University from 1881 until 1882 and was admitted to the South Carolina Bar in 1883. He began his practice in Laurens, but later moved to Spartanburg.
In 1890, he married Sarah Margaret Anderson of Laurens and they had five sons and three daughters. He was a member of the Methodist Church, the Knights of Pythias, and the Masons (Royal Arch), and the Shriners (Knight Templar).
He served as United States Congressman from 1901 until 1915. While a member of Congress, he was the ranking member of the House Appropriations Committee and Chairman of its Sub-Committee for all governmental functions except military and postal. He served as the “Watchdog of the Treasury.” He backed legislation to create the Federal Reserve Banks, to reform currence law, to eradicate pellagra, and to improve the Rural Free Delivery (RFD) mail system.
As a judge, his clear and simple rulings and instructions to juries typified his constant effort to do what was right. He always posed the moral side of any issue.