O’Neill, a reformer and minister of religion, was born in Chelmsford, Essex, in September 1819. His father, Arthur O’Neill, a coach maker, was an Irish protestant refugee, and his mother, Ann, claimed descent from John Rogers, a protestant martyr in Mary Tudor’s reign. The father died three months before Arthur’s birth, and the mother married an army quartermaster named Cooper. Destined for the army, O’Neill was employed by the 73rd regiment as a hospital dresser and compounder, during which time he attended the University of Malta and the college at Corfu. In 1835, he entered Glasgow University to study medicine but experienced a religious conversion and took up divinity.
As a student, O’Neill was influenced by J. A. Roebuck’s defence of the Canadians who rebelled in 1837; in his own words, he became ‘a peace man and a Chartist unchanged through nearly half a century’. During the late 1830s, he supported himself as a public lecturer and Chartist lay preacher. He was one of the leaders of the Christian Chartist movement which developed in Scotland. In 1840, he settled in Birmingham as the minister of a Christian Chartist chapel in Newhall Street. O’Neill’s insistence that Christianity should be ‘the sole standard of government, commerce, education, and of every other pursuit of man’ offended many Chartists. William Lovett attacked his ‘cant and sentimentality’ and Feargus O’Connor denounced Christian Chartism as a divisive force. His closest collaborators were John Collins and Henry Vincent, who shared his religiosity. He co-operated with Joseph Sturge and the ‘moral radical’ dissenters who devised a complete suffrage bill that incorporated the six points of the People’s Charter. After Lovett and O’Connor rejected the bill at a conference in Birmingham in December 1842, O’Neill continued to associate with Sturge and was increasingly identified with him. In the meanwhile, O’Neill had become involved in the strikes that swept across the midlands in mid-1842. He was prosecuted for sedition and conspiracy, tried in August 1843, and gaoled for nearly twelve months.
Imprisonment deepened O’Neill’s religious commitment and he wrote that henceforward he would work for ‘the speedy appearance of the kingdom of Christ’, as revealed by scripture prophecy. On his release he resumed his Christian Chartist ministry in Birmingham, but the development of his religious beliefs convinced him of the need for adult baptism by immersion, and in 1846 he became a Baptist minister. The new status did not abate his political fervour. He had joined the Peace Society before his imprisonment and from the mid-1840s, together with Joseph Sturge, Henry Richard, Elihu Burritt and Richard Cobden, he promoted arbitration as a means of resolving international disputes. Late in life, he attended peace congresses in European cities between 1889 and 1893. True to the ideals that had led to his imprisonment, he helped to set up trade unions and became a member of the Reform League during the 1860s. Towards the end of his life, he was calling, not only for the full implementation of the People’s Charter, but also for parliamentary suffrage for women ratepayers and a version of home rule that would devolve legislative powers on parliaments elected in all the regions of the British Isles including the midlands. He also opposed slavery, the Contagious Diseases Acts, and the regulations governing the religious aspects of public education. As a teetotaller for over half a century, he advocated temperance as part of a programme of working-class self-help.
A strong, burly man, O’Neill had ‘soft and tender-looking blue eyes’ and a mellifluous voice. Until very late in life he enjoyed excellent health. He married on 17th June 1845 Esther Piddock Fallows, who predeceased him by sixteen years. O’Neill died at his home, 55 Hall Road, Handsworth, Staffordshire, on 14th May 1896 of ‘a valvular trouble of the heart and a serious liver disorder’ and was buried in Handsworth Old Church beside his wife. Two daughters and a son survived him.
 Sources: Handsworth Herald and North Birmingham News, 16th May 1896, Birmingham Faces and Places, volume 2, (1889–90), pages 152–5, National Association Gazette, 8th January 1842, National Association Gazette, 12th February 1842, National Association Gazette, 18th June 1842, A. Wilson Scottish chartist portraits, 1965, A. Wilson The chartist movement in Scotland, 1970 and A. Tyrrell Joseph Sturge and the ‘moral radical party’ in early Victorian Britain, 1987.
 Birmingham Post, 24th November 1885.
 National Association Gazette, 18th June 1842.
 Letter from A. G. O’Neill, 3rd February 1844, Sturge MSS.
 Handsworth Herald and North Birmingham News, 16th May 1896.