Gresley began his engineering apprenticeship in 1893 under Francis Webb at the Crewe locomotive works, London and North Western Railway. Subsequently he was a pupil of John Aspinall of the Lancashire and Yorkshire Railway at Horwich, near Bolton; he then became an assistant manager at their carriage workshops at Newton Heath, Manchester, in 1901, and works manager in the following year. In 1904 Gresley was appointed assistant carriage and wagon superintendent of the L&YR, and, in 1905, he transferred to the Great Northern Railway in Doncaster as carriage and wagon superintendent. In 1911 Gresley succeeded Henry Ivatt as locomotive engineer then, in 1923, Gresley became chief mechanical engineer of the London and North Eastern Railway (LNER), following the merger of independent companies into four railway groups.