William Belcher was born in London, England, probably in 1859 or 1860, the son of Mary Ann Bull and her husband, William John Belcher, an engineer. Little is known of his early years before he went to sea in 1872. In his late teens or early 20s he may have been ship-wrecked on an island off the Great Barrier Reef. He then lived in Australia before settling in Port Chalmers, New Zealand, in 1879. Belcher became a crew member on the Jessie Niccol, supplying Joseph Hatch's sealing gangs on Macquarie Island, south-east of Tasmania. In 1882–83 he spent some months with a gang on the island, living on rabbits, penguins and penguin oil after Hatch failed to relieve them.
William Belcher's involvement with the union movement began after George Sangster arrived from Australia, and formed New Zealand branches of the Australian seamen's union in 1880. Belcher was absent on a trading voyage but he joined the union in 1882, by which time the Wellington and Port Chalmers branches had formed the Federated Seamen's Union of New Zealand (FSU). Following J. A. Millar's election as secretary in 1887, Belcher began to take an active role in the union. His 'sonorous voice' and 'ample proportions', no less than his strength and his pugilistic flair, made him a natural leader.
Belcher emerged into prominence on the eve of the 1890 maritime strike. He and an old friend, Jack Gibb, had not long been back from a seamen's conference in Sydney; strenuous efforts by them and Millar failed to prevent the strike from spreading to New Zealand. Belcher always believed that the shipping companies had planned to smash the union, and that had it not been for the marine engineers' failure to join the strike the men might have triumphed. As it was they 'were licked – and licked, and…were also kicked and kicked very hard indeed', as he later wrote. Wages were slashed. 'Victimisation was converted into a fine art', and Belcher was among those blacklisted.
After Millar won a seat in the House of Representatives, Belcher succeeded him in 1894 as secretary of both the local branch and the national body of the FSU, the former by now a small rump and the latter no more than a dream. Belcher also represented the seamen on Otago's powerful Workers' Political Committee (WPC) and joined the Knights of Labor. Because of his hostility to prohibition the Knights expelled him in 1895, prefiguring a schism in the WPC which cost all the Dunedin 'Lib–Lab' MHRs except Millar their seats in 1896.
Rebuilding the seamen's union and working for new labour laws preoccupied Belcher. The Union Steam Ship Company of New Zealand supported a company union, known derisively among unionists as the 'Deaf and Dumb Society'. However, few unionists realised the full potential of the Industrial Conciliation and Arbitration Act 1894 until the seamen's union forced the company to appear unwillingly before the Otago and Southland Board of Conciliation in February 1897. Despite the company's protests the board issued an award which increased wages. More important than this, however, was Belcher's success in using the new law to compel the company to recognise the union. Almost at once Belcher filed 'disputes' in other industrial districts. By 1900 his supporters controlled branches in all New Zealand ports. Only in Wellington did a rival organisation exist. The 'Deaf and Dumb Society' quietly faded away, finally terminating its own existence in 1911.
Over the next 10 years Belcher and his lieutenants – J. K. (Jack) Kneen in Auckland and W. T. (Tom) Young in Wellington – built a powerful national union. The managers of the Union Steam Ship Company now worked to establish a stable working relationship with Belcher (the fact that they were all based in Dunedin helped). Indeed, by 1906 the Court of Arbitration had replaced the company as the union's main bête noire because, having kept the seamen waiting for a year, it refused to give any increase in wages. Many seamen demanded that the union leave the arbitration system. Belcher shrewdly recognised, however, that the rival union in Wellington could then seek an award which would set pay rates and working conditions for the entire industry.
Belcher moved with cunning. He allowed a referendum on the issue of withdrawal and the men voted in favour. He then used this to persuade Millar, now minister of labour, and all the shipping companies that they should use an obscure clause in the arbitration act which allowed for collective bargaining. Belcher triumphed in 1908: the largest shipping companies were happy to match Australian or even British rates and conditions to buy peace in New Zealand. At the end of the year he persuaded the Court of Arbitration to register the agreement as an award, thus solving the problem of enforcement.
Belcher was at the height of his power and influence. He had supporters on all ships and in all ports, and the FSU boasted more than 2,000 members. His adversaries respected him even when they found his methods galling. In 1906 the government appointed Belcher to the Otago Harbour Board, and in 1907 he represented New Zealand at the colonial merchant shipping conference in London. Here he fought hard but unsuccessfully against the employment of non-white labour in the Australian and New Zealand shipping industry; he saw it as a ploy by the shipping companies to destroy the wages and conditions of the seamen. From 1909 to 1911 he waged a public campaign to keep Lascars out of New Zealand ports and off all visiting ships.
Belcher also became annoyed with his treatment by the harbour board. He told Jack Kneen that 'The brutes have treated me with contumely and contempt long enough. In the future they are going to fear me.' His subsequent behaviour won a succession of headlines. One chairman, driven to distraction, threw his pipe and an inkwell at the truculent 'old whale'. Belcher loved it all. So did the people, for when he sought election to the board in 1911 he headed the ticket and served as chairman in 1911–12. He had also been appointed a justice of the peace, a useful position for the FSU's secretary, and in 1912 he helped to negotiate a marked improvement in wages and conditions.
Fifty hard years had begun to exact a toll on Belcher. His health deteriorated, his eyesight began to fail, and he felt but 'a shadow of my former self'. Union politics were also changing. The wave of support for an independent and socialist New Zealand Labour Party did not appeal to the old sea dog, used to exercising influence within the Liberal caucus. Besides, he recognised that it would be some years before the Labour Party could occupy the treasury benches. He stood as an independent labour candidate for the Dunedin mayoralty in 1913, polling surprisingly well.
The balance of power within the seamen's union also shifted. Wellington supplanted Dunedin–Port Chalmers as the union's largest branch, and its able secretary, Tom Young, began attacking Belcher's power base. Young was also active in the Labour Party and accepted the presidency of the United Federation of Labour (UFL), formed in 1913, to which the FSU refused to be affiliated. When the UFL called a general strike in 1913, Belcher, who regarded strikes as suicidal, fought to keep the FSU neutral. After many seamen nevertheless joined the strike, he agreed to make it official. Within weeks, when it became clear that the strikers faced defeat, Belcher began manoeuvring to extricate the union on the best possible terms. His close working relationship with the leaders of the Union Steam Ship Company helped, and the FSU emerged stronger than ever. Other strikers complained of treachery.
Young had become the most powerful figure in the FSU, and supplanted Belcher as national secretary. Belcher buried his fury long enough to help reorganise the union in 1914–15, but his star was setting. He polled poorly in 1914 in his second bid for the mayoralty, having refused to campaign or offer a policy. Because many workers now opposed him he declined to accept Labour's nomination, in August 1914, for Dunedin Central.
Belcher took refuge in alcohol. In 1915, after being convicted and fined for assaulting his wife, he resigned as justice of the peace. In September 1915 he resigned from the harbour board, leaving behind 'an inky trail of abuse'. In 1917, amid allegations of misappropriation of funds, he retired as Dunedin branch secretary of the seamen's union. He then obtained employment with the Marine Department in Wellington. Belcher lived there uneventfully until his death on 15 June 1926. He was survived by his wife, Caroline Sayer, whom he had married at Dunedin on 3 May 1884, and two daughters.