The Unitarian Society was established in 1791. The term Unitarian began being used in Europe at the beginning of the 17th century. John Biddle (1615-62) is considered to be the first minister to establish a Unitarian congregation in Britain. Another early supporter was Theophilus Lindsey (1723-1808), who built the Essex Street Chapel in London in 1778. However, it was the Nonconformist minister and scientist, Joseph Priestley, who became the most important proponent of unitarianism in 18th century England. After his home was destroyed by a mob in 1791, Priestley emigrated to America.
The Unitarians drew their membership to a large extent from the scientific professions and their outlook tended to be rational and individualistic. The original intentions of the movement was to unite all Non-conformist groups but this ended in failure. There is no set doctrinal beliefs that all Unitarians agree on. In fact, the most important aspect of Unitarianism is the right of individuals to develop their own religious opinions. Therefore the bond between them consists more in their anti-dogmatism than in any uniformity of belief. However, Unitarians tend to believe that Jesus Christ was a human religious leader to be followed but not worshipped. Unitarians argued that Jesus is the "great exemplar which we ought to copy in order to perfect our union with God".
Unitarians believed that social evils were humanly created, not God inflicted, and therefore could be remedied by human efforts. Unitarians were strong advocates of democracy and argued that each congregation should manage itself without outside control. This included the power to select and discharge ministers.
In the the late 18th and early 19th century, Unitarians were closely identified with the campaign for social and political reform. Unitarians such as Joseph Priestley, Jeremy Bentham, Robert Wedderburn, Harriet Martineau, James Martineau and John Stuart Mill were all advocates of universal suffrage. Other leading radicals of the period such as Tom Paine and Thomas Muir were described by their critics as Unitarians. After the publication of Paine's The Rights of Man, religious radicals in London formed the Unitarian Society to promote the cause of parliamentary reform.
Unitarian congregations developed mainly in large industrial cities such as Manchester, Birmingham and Leeds. Growth was slow and by 1851 there were only 229 congregations with about 30,000 members. However, they had considerable influence owing to the prominence of Unitarians in British Industry (Josiah Wedgwood, John Marshall, Thomas Ashton, Samuel Fielden, George Courtauld, Samuel Courtauld, Peter Taylor, Samuel Oldknow, Henry Tate, Charles Booth, etc.) and in Parliament (John Fielden, Robert Hyde Greg and Peter Alfred Taylor).
James Martineau, the brother of Harriet Martineau, was the leading English Unitarian in the middle of the 19th century. In his book The Rationale of Religious Enquiry (1836), Martineau argued that "reason is the ultimate appeal, the supreme tribunal, to the test of which even Scripture must be brought". William Gaskell, a Unitarian minister in Manchester, and the husband of the novelist Elizabeth Gaskell, was another important figure during this period.
In the 19th century Unitarians were very active in the movements for factory reforn, public health, prison reform, temperance, women's rights and the abolition of slavery. Unitarian reformers included Edwin Chadwick, Florence Nightingale, Jenkin Lloyd Jones and Charles Booth.
In the religious census of 1851 there were 3,153,490 Protestant Nonconformists. This included 37,156 Unitarians.