O’Brien was born at Granard, co. Longford, Ireland, in early February 1804, the second son of Daniel O’Brien and his wife, Mary Kearney. His father, who was a wine and spirit merchant and a tobacco manufacturer in co. Longford, failed in business during O’Brien’s childhood, and died soon after. O’Brien was educated at the local parochial school and then at Edgeworthstown School, which had been promoted by Richard Lovell Edgeworth. He then went to Trinity College, Dublin, where he graduated BA in 1829. He entered the King’s Inns, Dublin, and then went to London, where he was admitted as a law student at Gray’s Inn in March 1830. In London he met Henry Hunt and William Cobbett.
In 1831, Henry Hetherington started up and edited the Poor Man’s Guardian, but O’Brien became its effective editor and also contributed to Hetherington’s Poor Man’s Conservative. He signed his articles ‘Bronterre’, and from this moment called himself James Bronterre O’Brien. At first O’Brien adopted many of William Cobbett’s views on the national debt and the currency, but soon he began to develop his own ideas. He read widely in the literature of the French Revolution, and visited France on three occasions in 1837–8. In 1836, his translated edition of Buonarotti’s History of Babeuf’s Conspiracy was published and in 1838 the first volume of his eulogistic Life of Robespierre appeared. By this time, O’Brien’s own opinions were insurrectionary and socialistic. In 1837, he began Bronterre’s National Reformer, but it soon failed and in 1838 The Operative that ended publication in July 1839. He had, meanwhile, married in the mid-1830s (the name of his wife is not known); he had four children.
From the beginning of the Chartist movement, O’Brien was one of its most prominent figures. He was a member of the original London Working Man’s Association, and was a delegate to the Chartist meeting in Palace Yard (17th September 1838) which opened the campaign in London. In 1838, he joined Feargus O’Connor at the Northern Star, and toured the country as a ‘missionary’ lecturer. Although regarded as a physical-force advocate, O’Brien was careful not to overstep the limits of the law. As he put it in the draft of the Chartist convention’s address (8th May 1839), ‘it was his intention to tell the people to arm without saying so in so many words’. He represented the Chartists of Manchester at the Chartist convention in the spring of 1839, and opposed the plan for a general strike.
As a result of the Newport rising of November 1839, a number of trials for sedition took place in the spring of 1840. O’Brien acted in his own defence and was acquitted at Newcastle in February on a charge of conspiracy, but was found guilty at Liverpool in April of seditious speaking. He was sentenced to eighteen months’ imprisonment. Towards the end of his sentence, O’Brien and Feargus O’Connor both began to communicate with the press, and carried on a controversy with one another as to the best policy for Chartists to pursue at the general election of 1841. O’Connor advocated an active alliance with the Conservatives, while O’Brien opposed this. Although still in prison, O’Brien stood as a Chartist candidate at Newcastle upon Tyne in the general election.
Released in September 1841, O’Brien continued the series of bitter personal quarrels with O’Connor, whom he later called ‘the Dictator’. O’Connor in turn nicknamed him the ‘Starved Viper’. O’Brien resumed his journalistic career, using various editorships to put forward his views on currency reform and continue his attack on O’Connor. He edited the British Statesman between June and December 1842, and in 1845 became editor of the National Reformer. During the Chartist campaign against the Anti-Corn Law League, O’Brien argued that free trade would lower prices, and so increase the proportion of the national wealth that landlords and owners of stock were able to appropriate. In the National Reformer he advocated ‘symbolic money’ and ‘banks of credit accessible to all classes’. He opposed O’Connor’s land scheme, and joined in with the moderate reform programme of the National Complete Suffrage Union.
O’Brien was one of the delegates at the Chartist convention which met on 4th April 1848. He spoke strongly against physical force. However, on 9th April, he withdrew from the convention on the grounds that the convention was likely to ‘go too fast’ and collide with the government. After the failure of the Chartist petition in 1848, O’Brien worked with G. W. M. Reynolds on Reynolds’ Political Instructor and Reynolds’ Weekly News. In October 1849, he used the former journal to launch his National Reform League, which advocated nationalization of the land and the monetary system. During the 1850s, O’Brien lived on his lecturing at the Eclectic Institute in Denmark Street, Soho, but never gave up the hope of more regular journalistic employment. His own weekly paper, the Power of the Pence, ran for five months during the winter and early spring of 1848–9, and during the following decade he hoped for work on papers as diverse as those of Reynolds, the Cobdenite Morning Star, and The Empire. O’Brien also remained politically active during the 1850s. He wrote several pamphlets on Lord Palmerston, Lord Overstone, Napoleon Bonaparte, and Robespierre. He was a member of the Stop-the-War-League during the Crimean War, travelled to Tiverton in April 1857 with the intention of contesting Lord Palmerston’s seat (he later withdrew), and in May 1858 established the National Political Union, which reiterated the call for the Charter. O’Brien’s later years were beset with poverty and alcohol-related illness. On several occasions, his books were seized for debt and in February 1862, Charles Bradlaugh lectured for the ‘Bronterre O’Brien testimonial fund’.
O’Brien died at his home in Pentonville, London, on 23rd December 1864. His wife survived him. In 1885, several of his followers published a series of his newspaper articles in book form, under the title of The Rise, Progress, and Phases of Human Slavery. As Graham Wallas noted, O’Brien was one of the few Chartists whose radicalism was the product of an original mind. Posterity has treated him unkindly. His alcoholism and embittered personal relationships leave the impression of a rancorous and impracticable politician. But he was one of the few non-Utopian socialists in England. He developed a vision of an alternative society which was based on a definitive programme of nationalisation of the land and of the monetary system. He was also probably the only Chartist who had any conception of popular insurrection and the means by which the labouring classes might appropriate power through a temporary dictatorship. For all his failings and idiosyncrasies O’Brien was a powerful character. He gained a large personal following among the artisans of Soho, who, in the aftermath of his death, became involved in both the Reform League and the First International.
 R. G. Gammage The history of the Chartist movement, from its commencement down to the present time, 1854, A. Plummer Bronterre: a political biography of Bronterre O’Brien, 1804–1864, 1971, S. Shipley Club life and socialism in mid-Victorian London, 1971 and M. Taylor The decline of British radicalism, 1847–1860, 1995.
 R. G. Gammage The history of the Chartist movement, from its commencement down to the present time, 1854, page 280.
 A. Plummer Bronterre: a political biography of Bronterre O’Brien, 1804–1864, 1971, page 191.