Gammage was born at Northampton. Following education at the Central national school and the Blue Coat charity school at Northampton, he was, at the age of twelve, informally apprenticed to a coach builder. He began his political career in 1837, when he joined the Working Men’s Association. He was a deputy to the national convention of 1838, and lectured in support of Chartist principles between 1842 and 1844. He settled at Northampton in 1844, and became Chartist secretary for that district; he thus came into frequent contact with Feargus O’Connor, whom he opposed. At this time Gammage earned his living as shoemaker. In 1848, after losing his employment at Northampton on account of his political opinions, Gammage moved to Birmingham. In 1852, he achieved national prominence by his nomination as Chartist parliamentary candidate for Cheltenham (though he did not go to the poll), and his election to the paid executive of the National Charter Association. Following a number of speaking tours in 1852–3, he failed to secure re-election having clashed with Ernest Jones, when he rejected the latter’s support for a labour parliament and co-operative enterprises on the land. In 1854, he published his History of the Chartist Movement (reprinted ed. J. Saville, 1969), a work reflecting his bias against O’Connor and Jones, and his indebtedness to Bronterre O’Brien’s social thought. The work is dominated by a one-sided interpretation of the tensions within the Chartist movement but remained a standard account for many years.
In May 1854, Gammage moved to Sunderland, where he worked as an insurance agent and lived with his brother Thomas Gammage (secretary of the Garibaldi committee). He joined the Newcastle foreign affairs committee (1854), the Newcastle committee for watching the war (1855), the National Reform Union, and the Northern Reform Union, and in 1866-7 he shared political reform platforms with Jones and Edmond Beales. In 1864, he qualified as a doctor and he went on to practise medicine at Newcastle and then Sunderland. He retired to Northampton in 1887, where he died at his home, 155 Wellingborough Road, on 7th January 1888, four days after falling from a tram. He left a widow, Sarah.
 Sources: F. D. Barrows and D. B. Mock A dictionary of obituaries of modern British radicals, 1989, page 165, J. Burnett The autobiography of the working class, ed. D. Vincent and D. Mayall, 3 volumes, 1984–9, pages 117–18 and M. Taylor, The decline of British radicalism, 1847–1860, 1995.