Garratt began his engineering career by serving an apprenticeship under John Carter Park, then locomotive superintendent of the North London Railway, from 1879-1882 at the North London Railway Bow works. Further experience found him serving at Doxford's marine engineering works in Sunderland, and later as an inspector for Sir Charles Fox and Sir Alexander Rendel. Garratt transferred to the Argentine Central Railway in 1889, where he became Locomotive Superintendent in 1892, and between 1900 and 1906 he worked for railways in Cuba, Lagos, and Lima (Peru). In 1902, Garratt was elected to membership of the Institute of Mechanical Engineers. He returned to England in 1906 and worked as an inspecting engineer for the New South Wales Government Railways.
Garratt's design for an articulated steam locomotive saw substantial usage in many in regions throughout Africa, South America, Asia, and the South Pacific where difficult terrain impeded railroad travel. In particular, the locomotive's articulated nature allowed it to navigate rail lines with sharp and frequent curves more easily than designs which lacked articulation. The ability to transverse previously impassable regions of land via railroad allowed for increased traffic of human activity and settlements, drastically reducing the isolated nature of previously remote areas of the world.
Additionally, the Garratt saw significant usage in economically developing countries due to extensive reliance on narrow gauge rail in these locales. The Garratt boasted high efficiency within its class and rail gauge, making its usage economically attractive in counties which would otherwise have to run larger numbers of locomotives per train or convert their existing rail lines to a larger gauge. This acted in part as an incentive for further rail expansion, and by extension, societal and economic expansion.