Hepburn appears on miners' banners alongside A.J. Cook and Arthur Scargill. The rapid growth of the Northumberland and Durham coalfields in the eighteenth century provided an arena for open trade unionism, but Hepburn's Union was the first true organisation among the miners. Hepburn, whose father had been killed in a pit accident, started work at Urpeth colliery in 1804. In 1831, we find him unable to form a union and the entire work force of the coalfield coming out on strike from March to August 1832. Hepburn held the men together through a lock-out lasting over two months. The union meetings were held in the Cock public house in Newcastle.
On 12 March, an immense number of pitmen gathered on the Black Fell near Ayton Banks in order to adopt resolutions and concert measures to raise wage levels. Another large meeting was held on the Town Moor in Newcastle on 21 March. Lord Londonderry was in a difficult position and represented a weak link in the owner opposition, and despite John Buddle's steadfast resistance, Hepburn secured a number of concessions, including a reduction in boys' working hours from fourteen to twelve. 'The Pitmen's Union' battle hymn of the Hepburn Union of 1830-32 ran:

Long, long, may Hepburn live;
Long may our union last.

Hepburn became a paid organiser for a time, but the union collapsed in the face of a determined counter-attack by the employers in 1832, who introduced non-union labour to replace the strikers and army units to enforce evictions. There was sporadic violence and in July 1832, Cuthbert Skipsey, father of Joseph Skipsey the poet, was shot dead by a policeman in a repulsed attack on Chirton High pit. The policeman received a six-moth sentence. In 11 June came the murder of 72-year-old Nicholas Fairless near Jarrow by two pitmen, of whom one, William Jobling was quickly tried and executed. The obsolete punishment of gibbeting was revived to turn Jobling's body into a terrifying symbol at Jarrow Slake. Sid Chaplin's powerful words convey the horror:

'Lifted up to be degraded, turned into a "white negro" covered from head to toe in pitch, strangely and fearfully encased in iron, he is transformed into a figure of almost archetypal power. A nonentity in life, he blossomed terribly in death.'

Hepburn held a mass meeting on Boldon Fell while the ritual of gibbeting was being enacted, and few were present at the Slake. Later on, Jobling's body was stolen and presumably given decent burial. The cholera had also arrived and the union was effectively finished. Both sides learned much from the episode, but Hepburn himself was forced into near destitution. Eventually a coal-owner offered him a job at Felling on condition that he never again joined a trade union. He accepted and worked there until he retired in 1859. Richard Fynes, the coalfield historian, described Hepburn as follows:
'Hepburn was not only a great leader among the miners, but his sympathies extended to the broad platform of politics. He was a man with a strong constitution, an intelligent mind, active and ever ready to lend a hand to any movement that had for its object the elevation of the people... He was one of the most active men in the Chartist agitation (q.v.). Fergus O'Connor, speaking of him, said: 'He is a noble specimen of human nature, and the people of the North of England have a right to be proud of him...' When the Miners Union was broken up, he spent a number of the remaining years of his laborious and useful life in agitating for parliamentary reform, and in educating the young ones with whom he came in contact.' Thomas Hepburn is buried in Heworth churchyard.