From Historic England entry:
“HISTORY: Conway Hall was built in 1929 as the headquarters of the South Place Ethical Society. The Society was previously based in a chapel in South Place, Finsbury and hoped that this new purpose-built hall would, in the words of a pamphlet issued in 1927: ‘enable the South Place Ethical Society to continue and increase its work and activities for a fuller and more vigorous moral, intellectual, and religious life… It is the aim of the Trustees and Committee to place at the disposal of the members and visitors from the Provinces, British Dominions, United States of America and other countries, Headquarters in the heart of London, where men and women of advanced thought could meet and enjoy the amenities of social discourse, with facilities for writing, rest and refreshment’. Plans were prepared for ‘a dignified and commodious building’ by a Society member, Frederick Herbert Mansford (1871-1946), a Licentiate of the Royal Institute of British Architects, and the hall was built at a cost of about £45,000. Its name was chosen in honour of Moncure Daniel Conway (1832-1907), an anti-slavery advocate, supporter of free thought and biographer of Thomas Paine. The choice of Bloomsbury as the location for the new hall may have been influenced by the area’s connotations of intellectual radicalism in the early C20, mainly through the reputation of the Bloomsbury Group circle of writers, artists and thinkers.
The society stemmed from a group of Christian dissenters and originally appointed ministers of religion as leaders. In 1888, however, it was renamed the South Place Ethical Society and hence became allied with a general movement promoting nontheistic religion established by Felix Adler in New York City in 1876 (although members at the time later forced the minister who had enacted the name change, Stanton Coit, to resign because they did not want to be part of the British branch of this movement). From 1897 the South Place Ethical Society appointed lecturers instead of ministers to deliver a Sunday address, preceded and followed by music. A number of ethical societies were established in the late C19 and early C20 in London, Cambridge and Cheltenham amongst other places, but the movement remained largely east-coast American in popularity. The South Place Ethical Society is the only remaining such society in the UK. In its early days it was connected with a number of important figures including Joseph McCabe, the secularist writer and lecturer, Herbert Burrows, a socialist reformer, and John Hobson, social theorist and economist.
Frederick Herbert Mansford was the architect of a number of schemes in London, including houses, offices and a restaurant on Earls Court Road in 1913, none of which is listed. Conway Hall was the most high-profile commission of his career.
The site of the hall was occupied by the Raglan Music Hall in the 1870s. This building was demolished before the end of the C19 and terraced houses built along Lambs Conduit Passage. These were cleared to make way for a second large building, possibly a hall, built in the Edwardian period, which was in turn replaced by Conway Hall in the 1920s. The site abuts one of the mid-late Victorian terraced houses on Theobalds Road which was adapted in 1929 to provide a second entrance to Conway Hall.”