Feargus O'Connor was born on 18 July 1794 in Connorville house, near Castletown-Kinneigh in west County Cork, into a prominent Irish Protestant family who claimed to be the descendants of the 12th-century king Ruaidrí Ua Conchobair. He was originally christened Edward Bowen O'Connor, but his Father chose to call him Feargus. His Father was Irish nationalist Politician Roger O'Connor, who like his uncle Arthur O'Connor was active in the United Irishmen. His elder brother Francis became a general in Simón Bolívar's army of liberation in South America. Much of his early life was spent on his family's estates in Ireland, which included Dangan Castle, the childhood home of the Duke of Wellington. He was educated mainly at Portarlington Grammar School and had some elementary schooling in England.

O'Connor's Father Roger was notorious for his eccentric lifestyle. At one point Feargus and Francis decided to leave, stealing horses from their brother Roderic, travelling to London and asking to be taken in by family friend M.P. Francis Burdett. Burdett looked after them, and financed Feargus to run a farm in Ireland, but it was unsuccessful. He studied law at Trinity College, Dublin, before inheriting his uncle's estate in 1820. He took no degree, but was called to the Irish bar about 1820. Since he had to take an oath of allegiance to the crown to become a member of the Bar, his Father disinherited him because he regarded it as inconsistent with the dignity of a descendent of the Kings of Ireland.

O'Connor's first known public speech was made in 1822 at Enniskene, County Cork, denouncing landlords and the Protestant clergy. During that year he composed a pamphlet State of Ireland. Around this time he was wounded in a fight with Soldiers, perhaps as a member of the Whiteboys covert agrarian organisation. Going to London to escape arrest, he tried to make a living by writing. He produced five manuscripts at this time, but none were ever published.

O'Connor was a superb public speaker. He expressed defiance, determination and hope, and flavoured these speeches with comic similes and anecdotes. He looked the part of a popular leader, too. His physique was to his advantage: over six feet, muscular and massive, the "model of a Phoenician Hercules". There is no doubt that the working people who heard O'Connor at these great meetings in the north of England in the late 1830s adored him.

In 1831 O'Connor agitated for the Reform Bill in County Cork, and, after its passage in 1832, he travelled about the county organising registration of the new electorate. During the 1830s he emerged as an advocate for Irish rights and democratic political reform, and a critic of the British Whig government's policies on Ireland. In 1832, he was elected to the British House of Commons as Member of Parliament for County Cork, as a Repeal candidate rather than a Whig.

As early as 1833, while MP for Cork, O'Connor had delivered an address to the National Union of the Working Classes, a political society of London working men, expressing radical sentiments. But O'Connor truly came into his own not when addressing audiences of London artisans or in the House of Commons, but when he went north as a public speaker.

He began to spend a large part of his time travelling through the north of England, addressing huge meetings, in which he denounced the 1834 Poor Law Amendment Act and advocated manhood suffrage. Only by securing the vote, O'Connor argued, could working people be rid of the hated New Poor Law.

In the general election of 1835 O'Connor was re-elected, but disqualified from being seated because he lacked sufficient property to qualify. However, it appears that he did have property valued at £300 a year. O'Connor next planned to raise a volunteer brigade for Isabella II of Spain in the First Carlist War, but when william Cobbett died in April 1835, he decided to run for Cobbett's seat at Oldham. Oldham was a two-member constituency and Cobbett's colleague John Fielden strongly advocated the Cobbett's son John Morgan Cobbett should be the Radical candidate to replace his Father. O'Connor presented himself as an alternative Radical candidate, but eventually withdrew, alleging Fielden had not been straightforward with him: whether because of the controversy over the selection of the candidate or the refusal of J M Cobbett to support disestablishment, Cobbett lost narrowly to a local ‘Liberal Conservative’.

The voice of the organization was O'Connor's newspaper, the Northern Star, which first appeared on 18 November 1837 in Leeds. It met with immediate success and was soon the most widely bought provincial newspaper in Britain. Its Editor was william Hill, a former Swedenborgian minister; Joshua Hobson was its publisher; and Bronterre O'Brien, former Editor of the Poor Man's Guardian, became the principal leader-writer. Perhaps the most popular part of the paper was Feargus' weekly front page letter, often read aloud at meetings; but the inclusion of reports of Chartist meetings from around the country and of readers' poetry were also vital sections of a paper made it a very important instrument in unifying and promoting the Chartist cause.

When the London Working Men's Association published the People's Charter in 1838, O'Connor and the Star endorsed it but not the London leadership. O'Connor was not ready to accept the political leadership of the London Working Men's Association. He knew that the workers wanted something more immediate than political education. He became the "constant travelling, dominant leader of the movement" He, not Lovett, became the voice of Chartism.

When the Chartist petition with 1,283,000 signatures was rejected by Parliament in summer 1839, tension grew, culminating in the Newport Rising. O'Connor was not involved in the planning of this event, though he must have known that there was a mood for rebellion among Chartists. He was a dangerous man to the authorities, and a sentence of 18 months in York Castle was passed on him in May 1840. In his farewell message, he made clear what he had done for the movement:

O'Connor was jailed; while in prison he continued to write for the Northern Star. He was now the unquestioned leader of Chartism. It was at this time that the song Lion of Freedom was published in his honour. It was widely sung at Chartist meetings. Lovett, meanwhile, left the movement, full of anger at O'Connor. But O'Connor's Energy and commitment was to keep Chartism alive for the rest of the 1840s.

Faced with the declining strength of Chartism after the defeats of 1842, O'Connor turned to the idea of settling working people on the land. While in prison, he had advocated just such a scheme in the Northern Star under the heading "Letters to the Irish Landlords". In 1835, he had given notice of his intention to introduce a bill to modify the rights of Irish tenants moved in Parliament. He later said his bill would have sought

When the first wave of Chartism ebbed, O'Connor founded the Chartist Cooperative Land Company in 1845. It aimed to buy agricultural estates and subdivide the land into smallholdings which could be let to individuals. The impossibility of all subscribers acquiring one of the plots meant it was considered a lottery, and the company was declared illegal in 1851.

O'Connor's Land Plan had its opponents in the movement, among them Thomas Cooper. On 24 October 1846 the Chartist Cooperative Land Company, later known as the National Land Company, came into being. A total of £112,100 was received in subscriptions, and with this six small estates were purchased and divided into smaller parcels. In May 1847 the first of the estates was opened at Heronsgate, renamed O'Connorsville. O'Connor's colleague Ernest Charles Jones wrote of this development:

In 1847 O'Connor ran for parliament and, remarkably, defeated Thomas Benjamin Hobhouse in Nottingham. But the Land Plan ran into trouble. When he had taken his seat he proposed in The Labourer that the government take over the National Land Company to resettle working people on a large scale. Those Chartist Leaders with whom he had quarrelled accused him of being "no longer a 'five point' Chartist but a 'five acre' Chartist." O'Connor replied to his critics at a meeting in Manchester. But the political elite was moving to crush O'Connor's Land Plan, declaring it illegal.

On 6 June 1848, the House of Commons investigation found that the National Land Company was an illegal scheme that would not fulfil the expectations held out to the shareholders and that the books had been imperfectly kept.

A man under huge pressure, O'Connor began to drink heavily. In July 1849, the House of Commons finally voted on the People's Charter, and rejected it by 222 votes to 17. In 1850 O'Connor once more made a motion in favour of the Charter, but would not be heard. The tragedy that was O'Connor's story was nearing its end.

O'Connor quarrelled with his closest colleagues, including Ernest Jones, Julian Harney and Thomas Clark. The circulation of the Northern Star fell steadily and it lost money. O'Connor's health was failing, and reports of his mental breakdown regularly appeared in the newspapers. In the spring of 1852 O'Connor visited the United States, where his behaviour left no doubt that he was not a well man. It is possible (though we have only the evidence of the unreliable diagnostic methods of the time) that O'Connor was in the early stages of general paralysis of the insane, brought on by syphilis.

In 1852 in the House of Commons O'Connor struck three fellow MPs, one of them Sir Benjamin Hall, a vocal critic of the Land Plan. Arrested by the Deputy Sergeant-at-Arms, O'Connor was sent by his sister to Dr Thomas Harrington Tuke's private Manor House Asylum in Chiswick, where he remained until 1854, when he was removed to his sister's house. He died on 30 August 1855 at 18 Albert Terrace, Notting Hill Gate. and on 10 September was buried in Kensal Green cemetery. No fewer than 40,000 people witnessed the funeral procession. Most Chartists preferred to remember O'Connor's strengths rather than his shortcomings.

From its inception the Anti-Corn Law League vied with the Chartists for the support of working people. Bread was dear, and the League claimed that repealing the taxes on import of grain would allow the price to drop. Chartists argued that without the Charter, a repeal of the Corn Law would be of little use. Other factors in their favour were the distrust by working people of anything supported by the employers, and the fear that free trade would cause wages to drop still lower. This last point was stressed by O'Connor. He made biting attacks on the Anti-Corn Law League. In some towns – for Example, Birmingham – O'Connorite Chartists broke up League meetings. O'Connor himself was certainly not afraid of taking on the Leaders of the League head-on in debate – in 1844 he took on Richard Cobden in Northampton.