Founded in 1791 by WS Bourne, The Observer is the world's oldest Sunday newspaper. Initially the paper lost money, and Bourne attempted to sell it to the government of the day. They declined, but the newspaper survived. Over the course of the next century, The Observer became increasingly sober, steering away from the gossip and government propaganda that were a feature in its early years.

High-profile moments in the paper's history included proprietor William Innell Clement reporting on the criminal proceedings against the Cato Street Conspirators, despite a government ban, and the exposure of Count Esterhazy's forgery of letters leading to the Dreyfus Affair.

From 1891 until 1903 The Observer was edited by Rachel Beer, whose husband Frederick Beer was then the proprietor. Beer became the first woman to edit a national newspaper, and from 1893, combined the role with that of editor The Sunday Times.

Lord Northcliffe acquired The Observer when Frederick Beer died in 1903. He appointed JL Garvin as editor. Under Garvin circulation rapidly increased from 5000 to 40,000, however political differences between Northcliffe and his editor led to the sale of the paper to William Waldorf Astor in 1911. Astor transferred ownership to his son, who in turn transferred it to his son David Astor in 1948. David Astor became the paper's editor, remaining in the role for 27 years. He tried to ensure The Observer's political neutrality, handing ownership to a trust.

Under David Astor contributors to the paper included George Orwell, Conor Cruise O'Brien, the notorious Kim Philby, photographers Don McCullin (freelance) and Jane Bown.

Between 1977 and 1993 the paper was owned by two large international companies, first Atlantic Richfield and then Lonhro. Increasing competition after the foundation of rival paper The Independent on Sunday eventually saw The Observer bought by the Guardian Media Group in 1993.

Changes since 2000 included moving to the Berliner format and becoming the UK's only full colour Sunday newspaper in 2006, being the first newspaper to record its own decisions via a blog from 2005 and the first to create a podcast.

In late 2008 The Observer moved to new offices shared with The Guardian in King's Cross, London.