The Peacock Theatre (previously the Royalty Theatre) is a West End theatre in the City of Westminster, located in Portugal Street, near Aldwych. The 999-seat house is owned by, and comprises part of the London School of Economics and Political Science campus, who use the theatre for lectures, public talks, conferences, political speeches and open days. The theater is currently performing the musical Jim Steinman's Bat Out of Hell. It’s electrified audiences in London, New York, Toronto and Germany, and won the audience-voted Evening Standard Award for Best New Musical.

The university has a long lease with London's principal centre for contemporary dance, Sadler's Wells, with whom it has negotiated a deal to bring in dance companies under the banner 'Sadler's Wells in the West End'. The venue often plays host to dance performances, conferences, ballet, pop concerts and award ceremonies.

The present, smaller theatre was built and christened The Royalty Theatre in 1960, located on the ground level of an office building. It was the first West End theatre to be built since the Saville Theatre in 1931. The first production was of a Friedrich Dürrenmatt play, The Visit, with Alfred Lunt and Lynn Fontanne. In March 1961 it hosted the William Gibson play about Helen Keller, The Miracle Worker.

Later in 1961, MGM leased the theatre to continue the run of the film Ben Hur following closure of the Empire, Leicester Square for rebuilding. This ran from 29 May 1961 to 6 May 1962, after which the theatre was closed until 19 November 1962 when Mutiny on the Bounty opened. This ran until 10 July 1963, and following a few weeks of revivals (Quo Vadis and Gigi) MGM closed the theatre on 3 August.

The lease was taken over by the Cinerama Corporation and the theatre was then equipped for screening three-strip Cinerama films becoming London's third Cinerama theatre (the others being the Casino Cinerama and the Coliseum Cinerama). The first presentation was The Wonderful World of the Brothers Grimm which transferred from the Coliseum on 27 November 1963. A compilation film entitled The Best of Cinerama ran for eleven weeks from 22 March 1964, after which the theatre was converted to 70mm single lens Cinerama to take over the run of It's a Mad Mad Mad Mad World from the Coliseum on 16 July. The theatre only premièred one Cinerama film, The Golden Head, which opened on 8 April 1965 and ran until 29 July. From 30 July The Greatest Story Ever Told transferred from the Casino Cinerama and ran until 27 October. From the 29th, The Royalty commenced a run of My Fair Lady which was still showing at the Warner Leicester Square. This ended on 29 June 1966 to be followed by a revival of Mediterranean Holiday until 7 August when Cinerama pulled out and the theatre closed.

The lease was picked up by Gala Film Distributors and the Royalty reopened on 1 December with the X-rated Swedish film Night Games. Gala continued with a combination of foreign films and mainstream revivals until 19 December 1969 when the theatre closed as a cinema for the last time and returned to live theatre use. The Royalty Theatre's only successes were a run of the hit Oh! Calcutta! and a hit production of Bubbling Brown Sugar in the late 1970s. It was also the venue for the first and last concerts on what turned out to be the final tour of the English folk-rock singer Sandy Denny with her band in November 1977, and the venue features on the 1998 posthumous release Gold Dust which was produced over 20 years later from the original tapes. Spectacular 'follies' style shows and 'drag' shows didn't find an audience, and the theatre became used as a TV studio for This Is Your Life, but was later bought by the London School of Economics and renamed the Peacock Theatre.

When Sadler's Wells determined to build its new theatre in 1996, the company moved to the Peacock Theatre. After the new Sadler's Wells Theatre opened in 1998, the Peacock became a dance venue for the company. The Rat Pack played at the theatre in 2002, and Doldrum Bay premièred here in 2003. The house is now shared between the London School of Economics (during the day) and Sadler's Wells evening dance productions.

The Peacock Theatre is most noted as the home of one of the West End's most unusual ghosts, a dolphin commonly known as 'Flipper'. An urban myth has grown up that, during one of Paul Raymond's revues at the theatre in the 1970s, a dolphin was kept in a tank beneath the stage, where it lived permanently and later died from neglect. In fact, this is not true. Two dolphins called 'Pennie' and 'Pixie' were indeed kept in a tank at the theatre for three months for a show called 'The Royalty Folies', which was later renamed 'The Great International Nude Show'. However, neither of these animals died while at the theatre and at the close of the show the animals were moved to a dolphinarium in the East Asia.

The remnants of the tank and its lifting equipment still remain below the stage and numerous visitors to the theatre claim to have heard in the vicinity a spectral squeaking, not unlike a crying baby. One possible explanation is that the London Underground Piccadilly line Aldwych spur used to pass very close to the sub-stage areas of the theatre and it is noise from the tunnels that created the sound.