George Rennie, the son of John Rennie, was born in 1791. John Rennie was a successful engineer and had been responsible for building Waterloo Bridge and Southwick Bridge in London.

After the death of John Rennie in 1821, George and his brother John (1794-1874) became partners in the family engineering firm. In 1826 the two Rennie brothers and Charles Vignobles surveyed the Liverpool & Manchester line and were invited by the company to build it. However, they refused to work with George Stephenson, who they did not consider was a real engineer, and they lost the contract. Rennie also laid out the route for the London & Brighton Railway but the company decided to give the job of building it to John Rastrick.

In 1838 George and John Rennie established a company in London and during the next four years built 16 locomotives. None of these locomotives were very impressive and with trade declining, George turned successfully to marine engineering. George Rennie died in 1866.