In 1848 Adams became assistant works manager for Philip Taylor, an ironfounder, millwright and former assistant to Marc Brunel, who had set up workshops in Marseilles and Genoa to build and install marine engines. Fluent in French and Italian, Adams soon found himself effectively the superintendent engineer for the Royal Sardinian Navy, although still nominally working for Taylor. (The Kingdom of Sardinia then encompassed Genoa and much of what is now north-west Italy.) In 1852 he married Isabella Park, the daughter of another English millwright working in Genoa, and returned to England.
On his return to England Adams initially worked as a surveyor: considering possible routes for a railway on the Isle of Wight, overseeing construction work at Cardiff Docks and planning and equipping new workshops at Bow for the East & West India Docks & Birmingham Junction Railway, soon to change its name to the North London Railway. This led to his appointment as the company's locomotive engineer in 1854, a post he held for eighteen years. Here he introduced his noted series of 4-4-0 tank engines, the first to utilise the laterally-sprung bogie, and the first continuous train brake.
In 1873 Adams took up a similar position with the nearby Great Eastern Railway. There he did not well appreciate the different requirements of the line, a far-flung concern compared with the North London, and his locomotive designs for the company were found to be underpowered for main-line work. However his refitting of the company's Stratford works using modern, standardised equipment saved a great deal of money and, when he left for the London and South Western Railway in 1878, his reputation was intact.
On the LSWR he designed 524 locomotives, supervised the expansion of Nine Elms Works and the transfer of the Carriage and Wagon Works to Eastleigh. Failing health forced his retirement on 1895-05-29. He lived in Putney until his death on 1904-08-07.