For more than three decades, Rodney Bickerstaffe, who has died aged 72, was one of the best known faces of the British trade union movement. Bickerstaffe, or “Bick” as he was almost universally known, was immediately recognisable by his dark, heavy-framed NHS spectacles and a shock of hair that had many comparing him with Buddy Holly. His tough, uncompromising oratory often held Labour and trade union conferences spellbound, but behind these rhetorical masterpieces, ferociously denouncing inequality and poverty wages, was a highly thoughtful, pragmatic and strategic union leader who could be mixing it with Arthur Scargill one day and Tony Blair the next.

Bickerstaffe commanded loyalty and affection among the low-paid workers he fought for and represented, first as general secretary (1981-93) of the National Union of Public Employees (Nupe), then as associate general secretary and general secretary (1993-2001) of Unison, one of Britain’s largest unions, with 1.3 million members. Unison resulted from the first major trade union merger – between Nupe, the white-collar union Nalgo and the health workers’ union Cohse – which was engineered by Bickerstaffe, who believed that Nupe’s overwhelmingly low paid, blue collar membership could only benefit by coming together with the other more powerful unions.

It was he, more than anyone else, who took up the cudgels for a basic minimum wage for all workers following the winter of discontent of 1978-79, when public sector workers went on strike against the Labour government’s social contract. For not only did poorly paid public sector workers not benefit from their protracted strike against the pay caps set by James Callaghan’s government, but its subsequent collapse heralded the election of Margaret Thatcher and the Conservatives.

Bickerstaffe, who had come to national prominence at that time, anticipated the all-out assault on the ability of the trade union movement to organise and negotiate. He saw that the binmen and gravediggers – his members – had become useful scapegoats for Fleet Street editors focused on uncollected rubbish and the unburied dead.

According to his longtime colleague in Nupe, Lord (Tom) Sawyer, Bickerstaffe believed that a minimum wage was absolutely essential to offer basic protection to the poorest paid. Yet at that time, it was opposed by many other trade unions, especially those in the manufacturing sector, in the belief that it aimed a dagger blow at wage differentials. Bickerstaffe would turn up urging a minimum wage at meetings attended, if he was lucky, by one man and a dog.

Two decades later, the national minimum wage was introduced in April 1999 by Blair, a Labour prime minister with whom Bickerstaffe had little in common, yet for entirely practical and pragmatic reasons, maintained a good-natured working relationship. On one occasion, nearing his retirement, Bickerstaffe and his wife, Pat, were invited to Chequers, the prime minister’s country residence, for lunch. After the meal, an intermediary quietly informed him that Blair wished to offer him a peerage. He immediately and politely declined.

Rodney Bickerstaffe in June 1982 Photograph: Tony Martin/The Observer

Bickerstaffe was born in London, towards the end of the second world war. His mother, Elizabeth Bickerstaffe, a union activist from South Yorkshire, had been finishing her nursing training at Whipps Cross hospital in the heavily bombed East End during the blitz. Rodney was the result of a wartime romance. His father, Tommy Simpson – whom he never met – returned to Dublin and ceased all contact with the family.

Much later, in the 1990s, Bickerstaffe’s quest to find his father finally led to his mother revealing his possible whereabouts. Tommy had died in 1991 but Bickerstaffe’s subsequent discovery of three half-brothers and a whole Irish family was not only a cause of huge delight to him, but helped further cement a long friendship with the former international development secretary, Clare Short, as she was reunited with her lost son, Toby.

Bickerstaffe’s family tree can be traced back to the village of the same name near Ormskirk in Lancashire. At one time his mother’s family were so poor they lived in a Gypsy caravan in a field. Unsurprisingly, given his unstinting championing of the underdog, Bickerstaffe was one of the few public figures to loudly champion the cause of Travellers over the years.

When he was still a small boy, his mother moved back to Yorkshire, and Bickerstaffe grew up in Doncaster. He went to Doncaster grammar school and studied sociology at Rutherford College of Technology (later part of Newcastle Polytechnic, now Northumbria University). His mother recruited her student son into the union movement and his rise was meteoric. He became a Nupe official in his late 20s and, moving from Yorkshire as an area officer to Newcastle, and later to London, Bickerstaffe launched a major campaign to recruit women to the union before becoming its local government officer in the dog days of the Callaghan government. He was appointed general secretary in 1981.

During the bitter year-long miners’ strike of 1984-85, Bickerstaffe, along with Bill Keys, of the printworkers’ union Sogat, played a key role behind the scenes in offering support and battling for a settlement aimed at avoiding the mass closure of the coalfields. Bickerstaffe was one of the few who could talk directly to Scargill.

Such was the concern among the trade union leadership that a combination of the obduracy of Scargill and Thatcher could end in a complete defeat for the miners that Moss Evans, general secretary of the Transport and General Workers Union, and Clive Jenkins, of the white collar ASTMS union, decided to try to have Bickerstaffe become TUC general secretary. But Bickerstaffe decided against, and Norman Willis duly assumed the post. Bickerstaffe, despite all attempts to get him to do so, would never betray his loyalty to the National Union of Mineworkers and indeed to Scargill, whatever his private misgivings about the latter’s strategic failings.

Bickerstaffe surprised many when he announced his retirement from Unison at the age of 55, but in reality it was not a retirement at all. At the Labour party conference in 2000, he moved the successful resolution that linked the rise in pensions with earning or prices, whichever is higher, and in 2001 he succeeded Jack Jones as president of the national pensioners convention, which champions the rights of Britain’s 11 million pensioners.

He became a passionate advocate of Palestinian rights, and president of War on Want, and chaired the Ken Gill Memorial Fund, dedicated to promoting the values of his old friend Gill, the internationalist and trade union leader. When union officials would turn to him in times of difficulty and stress, Bickerstaffe would invariably lift their spirits with what became something of a catchphrase: “Keep on keeping on.”

In the years since his retirement Bickerstaffe had also been transferring papers, mementoes and videos to the Rodney Bickerstaffe Archive at the Modern Records Centre at Warwick University. Recently he expressed regret that he had not completed this mammoth task.

Bickerstaffe is survived by Pat and their four children.

• Rodney Kevan Bickerstaffe, trade unionist, born 6 April 1945; died 3 October 2017