Leach was born in Wigan, Lancashire. His family origins and early years are entirely unknown, although it may be that he was an Anglican and that he had worked as a hand-loom weaver. He moved to Manchester in 1826; and in 1839, when he led the resistance to a cut in wages, he was sacked as a power-loom weaver after twelve years in the same employment. According to Friedrich Engels, however, who described him as ‘my good friend’, Leach had ‘worked in various branches of industry both in factories and coalmines’.
Leach was to claim in 1851 that he had been politically active for twenty years. By 1836, he was chairing meetings of the Manchester Radical Association, in 1838 he was elected to the council of the Manchester Political Union, and during the following year he began to represent Manchester at regional Chartist meetings. Given this local radical prominence, it made excellent sense for him, on losing his job, to set up as a bookseller and printer in Oak Street, Manchester. It was at this time, however, that his Chartist career moved on to the national level. In July 1840, he chaired the delegate conference in Manchester at which the key organisation of Chartism, the National Charter Association, was established. He was subsequently appointed provisional president and in both 1841 and 1842 came second only to Peter Murray M’Douall in the national elections to the executive. He sat as a delegate in the 1842 convention, of which he acted as vice-chairman.
According to Gammage, the Chartist activist and historian, Leach “never attempted to play the orator. In addressing a public meeting he was just as free and easy as in a private conversation; but for fact and argument there were but few of the speakers at that period who excelled him.”. His reputation was as a ‘terror, not only to the cotton lords, but every other humbug’. To O’Connor, he was a ‘plain blunt man’; and Engels considered him ‘upright, trustworthy and capable’ and drew extensively upon his 84-page pamphlet Stubborn Facts from the Factories by a Manchester Operative (1844) in The Condition of the Working Class in England.
Leach played a prominent part in bringing Chartism and the trade unions together, notably in support for the general strike movement of August 1842, and was one of the fifty-nine defendants in the mass trial at Lancaster in March 1843, although, like the others found guilty of conspiracy, he was not sentenced. He continued as a leading Chartist throughout the 1840s, but was also active in the co-operative movement (while not an Owenite) and in the agitation for a ten-hour limit on the working day. It had been in a series of open letters to Leach that O’Connor had, during his imprisonment of 1840–41, begun to develop his ideas about the centrality of land ownership to the emancipation of the working class, and in due course Leach too became an enthusiastic advocate of the Chartist Land Company, serving from 1845 as one of seven trustees. In 1848, he was a member of both the national convention of April and the national assembly of May and the latter appointed him to the militant provisional executive. A committed supporter of collaboration between English Chartists and Irish confederates, he had represented the Chartists in Dublin on 12th January at the first meeting between the two movements. From July 1848, he was printer, publisher, and co-editor of the English Patriot and Irish Repealer, which ended with his prosecution in December on another charge of conspiracy, for which he was sentenced to nine months’ imprisonment in Kirkdale gaol.
After his release, from late 1851 Leach came to favour an alliance with the middle-class radicals, a startling U-turn for one who had displayed continuous personal and ideological hostility towards the Anti-Corn Law League. This phase was short-lived as he soon retired from politics and returned to the obscurity from which Chartism had lifted him. His wife, Hannah, who died on 17th August 1865, may have been the Hannah Hurst who married a James Leach in Burnley, Lancashire, on 4th September 1826. It is known that they had five children, of whom the first son was named Alexander. Leach gave up his printing and bookselling business to manufacture soft drinks, and on his death at Eagle Street, Hulme, Manchester, on 4th July 1869 his occupation was given as ginger beer maker.
 Sources: E. Frow, R. Frow, and J. Saville, ‘Leach, James’, Dictionary of Labour Biography, volume 9 and S. Roberts Radical politicians and poets in early Victorian Britain: the voices of six chartist leaders, 1993.
 F. Engels The condition of the working class in England, ed. and trans. W. O. Henderson and W. H. Chaloner, 2nd edition, 1971, pages 151–2, 342.
 R. G. Gammage History of the Chartist movement, 1837–1854, new edition, 1894, page 211.
 P. A. Pickering Chartism and the Chartists in Manchester and Salford, 1995, page 199.
 F. Engels The condition of the working class in England, ed. and trans. W. O. Henderson and W. H. Chaloner, 2nd edition, 1971, page 152