Robert Barr was born in Barony, Lanark, Scotland to Robert Barr and Jane Watson. In 1854, he emigrated with his parents to Upper Canada at the age of four years old. His family settled on a farm near the village of Muirkirk. Barr assisted his father with his job as a carpenter, and developed a sound work ethic. Robert Barr then worked as a steel smelter for a number of years before he was educated at Toronto Normal School in 1873 to train as a teacher.

After graduating Toronto Normal School, Barr became a teacher, and eventually headmaster/principal of the Central School of Windsor, Ontario in 1874. While Barr worked as head master of the Central School of Windsor, Ontario, he began to contribute short stories-often based on personal experiences, and recorded his work. On August 1876, when he was 27, Robert Barr married Ontario-born Eva Bennett, who was 21. According to the 1891 England Census, the couple appears to have had three children, Laura, William, and Andrew.

In 1876, Barr quit his teaching position to become a staff member of publication, and later on became the news editor for the Detroit Free Press. Barr wrote for this newspaper under the pseudonym, "Luke Sharp." The idea for this pseudonym was inspired during his morning commute to work when Barr saw a sign that read "Luke Sharp, Undertaker." In 1881, Barr left Canada to return to England in order to start a new weekly version of "The Detroit Free Press Magazine."