Born in Law Wynd in Falkirk, the eldest of five children of John Walker and his wife Margaret, James was educated at the local school and was sent to Glasgow University in October 1794, aged 13. He studied Latin and Greek for two years, and logic during his third year. During his final two years he studied natural philosophy and mathematics, taking the first prize.
He returned to Falkirk in May 1799, aged 18, and his family discussed a career in business or law. But, by chance, in the summer of 1800, he was asked to accompany his ill brother-in-law on a sea journey to London. Once there, he visited his uncle Ralph Walker in Blackwall, intending to return to Scotland after a week. However, Ralph discussed his work at the West India Docks, and was so impressed by his young nephew's grasp of engineering that he immediately took him on as his apprentice.
Around 1800 they worked on the design and construction of London's West India and East India Docks. At the age of 21 he took on his first engineering work in his own right: the construction of Commercial Road in London, connecting the West India Docks to the warehouses of the City. Later, he worked on the Surrey Commercial Docks from about 1810 onwards, remaining as engineer to the Surrey Commercial Dock Company until his death in 1862.
Walker was the senior partner of the consulting engineering firm of Messrs. Walker and Burges (of Limehouse), Burges having first became his pupil in 1811 and risen to partner in 1829. In 1832 their offices moved to 44 Parliament Street, Westminster (which lies at southern end of Whitehall) and then to 23 George Street. In 1853 he promoted James Cooper, one of his assistants, to the partnership with the firm then being known as Messrs. Walker, Burges & Cooper.
Walker was also involved in designing a dock harbour in Hamburg (1845, with William Lindley and Heinrich Hübbe). He was also involved in the Liverpool and Manchester Railway, preparing a report on the merits of stationary and locomotive engines along with other notable engineers of the day. He was also for a long period consulting engineer to the Board of Admiralty.
^William, Thomas (1900). Life of Sir James Nicholas Douglass. London: Longman, Green and Co. p. 65. The firm of which this eminent man was head, whose offices were in Great George Street, Westminster, had long been carried on under the style of Walker, Burges & Cooper...Mr. James Cooper, the junior partner
^ ab"The Whitby Gazette". 22 May 1858. p. 4. Messrs. Walker, Burgess, and Cooper, of Great George Street, London, are the engineers
^"The Leipzig-Dresden railway line through time". Archived from the original on 11 November 2013. Walker, embarked on his journey to Saxony and arrived in Leipzig on 13 October 1835 with his assistant, John Hawkshaw. They spent nearly two weeks looking over the countryside between Leipzig and Dresden
^"Messrs. Mitchell and Sons Screw-pile Battery, and Light-House", Belfast News Letter, p. 1, 30 January 1844, That the first of such foundations was fixed on the Maplin Sands by these engineers (Messrs. Mitchel and Son), in the summer of 1838 by order of the corporation of Trinity House, at the recommendation of their engineer, James Walker, Esq. F.R.S., &c. Who has since erected on it the Maplin lighthouse