The school was founded in 1830 by University College London and inherited many of that institution's progressive and secular views.

Continuing on the long tradition of dissenting academies, the University of London had been inspired by the work of Jeremy Bentham and others to provide opportunities for higher education regardless of religious beliefs.

[2] At the time, only members of the established Church could study at Cambridge and Oxford (the only other two universities in England at the time) while similar religious tests were imposed at the other universities dating from the medieval and renaissance periods present in the rest of the British Isles, namely St Andrews, Glasgow, Aberdeen, Edinburgh and Dublin.

Several of the founders of the University of London are directly associated with the founding of the school; they include Henry Brougham, 1st Baron Brougham and Vaux (who appears to be singled out as the ring leader in A tradition for Freedom), Lord Auckland (probably George Eden, 1st Earl of Auckland), William Bingham Baring, 2nd Baron Ashburton, Sir Isaac Lyon Goldsmid, Henry Hallam, Leonard Horner (The Royal Society of Edinburgh has described UCS as his 'monument'[3]), James Mill, Viscount Sandon (probably either Dudley Ryder, 1st Earl of Harrowby or Dudley Ryder, 2nd Earl of Harrowby), James Lock, Stephen Lushington D.C.L.

The first headmaster was Henry Browne, who quickly caused controversy, by publishing a prospectus for the school which appeared to include some type of communal worship.

By February 1831 it had outgrown its quarters, in October 1831, the council of UCL agreed to formally take over the school and it was brought within the walls of the college in 1832, with a joint headmastership of Professors Thomas Hewitt Key and Henry Malden.

UCS moved to new purpose-built buildings in Frognal in Hampstead in 1907, which were opened by Edward VII with the Archbishop of Canterbury in attendance on 27 July.

[4] Prince Edward, Duke of Kent, opened the Sixth Form Centre (which also houses the Lund Theatre) in 1974.

Elizabeth II visited the school in 1980 to celebrate its 150th anniversary and to inaugurate the rebuilt hall, which had been destroyed by fire in 1978.

The five houses are: Bannister (black), Bonnington (silver), kendall (blue), MacArthur (green), Seacole (yellow).