John Roebuck, the second of five sons of John Roebuck (c.1680–1752), a successful merchant, was born in Sheffield in 1718. After studying at the University of Edinburgh he became a physician. He moved to Birmingham where he set up a scientific laboratory. According to his biographer, R. H. Campbell: "Initially his activities were on a small scale, carried on from his own house and in his spare time, but they led to a series of inventions which proved useful in local manufactures, especially in the refining of gold and silver. They also showed the need for greater financial resources and wider commercial acumen than Roebuck possessed if his ideas were to bear fruit. This need led him into several partnerships throughout his life. The first, one of the few which brought Roebuck considerable financial success and launched him on subsequent ventures, was when he and Samuel Garbett (1717–1805), a successful entrepreneur in Birmingham, set up a refinery in Steelhouse Lane."
His research led to improvements in methods of refining precious metals and in the production of chemicals. In 1749 Roebuck and Samuel Garbett began the manufacture of sulphuric acid on a large scale at Prestonpans near Edinburgh. This acid replaced sour milk as a means of bleaching cloth.
In 1759 Roebuck, Samuel Garbett and William Cadell established the Carron Ironworks near Falkirk in Scotland. They also purchased nearby coal mines to provide fuel for his ironworks. The mines suffered from severe flooding and he recruited James Watt to help him build an engine to pump out the water. In 1763 Watt was sent a Newcomen steam engine to repair. While putting it back into working order, Watt discovered how he could make the engine more efficient. Watt worked on the idea for several months and eventually produced a steam engine that cooled the used steam in a condenser separate from the main cylinder. James Watt was not a wealthy man so he asked Roebuck to provide financial backing for the project. Roebuck agreed and the two men went into partnership. Roebuck held two-thirds of the original patent (9th January 1769) in return for discharging some of Watt's debts.
R. H. Campbell has argued: "The conception of the scale of the works and the adoption of modern methods of production may be attributed to Roebuck. They were to prove enormously beneficial in due course, but not immediately; what was evident much sooner was the inadequacy of the initial capital stock of £12,000. To enable the concern to continue, funds had to be sought from banks, by the introduction of new partners, and, with consequences which proved nearly fatal a few years later, by the issuing of short-term accommodation bills. Using short-term credit brought the company to the verge of collapse in the financial crisis of 1772."
In March 1773 Roebuck became bankrupt. At the time he owed Matthew Boulton over £1,200. Boulton knew about Watt's research and wrote to him making an offer for Roebuck's share in the steam-engine. Roebuck refused but on 17th May, he changed his mind and accepted Boulton's terms. James Watt was also owed money by Roebuck, but as he had done a deal with his friend, he wrote a formal discharge "because I think the thousand pounds he (Boulton) he has paid more than the value of the property of the two thirds of the inventions."