The Chartist was born in Northampton. He was a deputy to the national convention of 1838, and lectured in support of Chartist principles between 1842 and 1844. In 1848 he moved to Birmingham and 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. In 1854 he published his History of the Chartist Movement , a work reflecting his bias against O'Connor and Jones, and his indebtedness to Bronterre O'Brien's social thought. The work 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. In 1864 he qualified as MRCS, and he went on to practise medicine at 18 Villiers Street, Bishopwearmouth.