Established in 1938, as the Assembly Rooms for Watford Town Hall, the complex was extended in 2011 with improvements which included new meeting spaces, a new restaurant and new bar facilities.

The Colosseum is also an important venue for boxing matches with heavyweight boxer Tyson Fury building on his reputation, shortly after turning professional, in 2009.

[10] The venue boasts a pipe organ, designed and built by John Compton, which was removed from the Gaumont Palace in Chelsea when it was modernised in 1960 and instead installed at the Colosseum.

[13] The first album, Puccini Heroines, included excerpts from Manon Lescaut, La bohème, Madama Butterfly, Suor Angelica, Gianni Schicchi and Turandot.

[13] The second album, Lyric & Coloratura Arias, included excerpts from Rossini's The Barber of Seville, Verdi's I vespri siciliani, Meyerbeer's Dinorah, Boito's Mefistofele, Delibes's Lakmé, Catalani's La Wally, Giordano's Andrea Chénier and Cilea's Adriana Lecouvreur.

[14] In June 1995 the tenor, Luciano Pavarotti, who had a house in Pesaro, agreed to visit the Colosseum where, supported by the Philharmonia Orchestra, he recorded Hymn of the Nations by Giuseppe Verdi.

[19] In October 2011 a charity concert, involving Zulu warriors, Ghanaian acrobats and Masai cultural dancers was held at the venue in order to raise funds for an appeal following the 2011 East Africa drought.

[20] The rapper, singer, songwriter and record producer, Ms. Dynamite, arranged a function in support of Great Ormond Street Hospital at the venue in April 2012,[21] although that particular event had to be moved at the last minute because of a leaking roof.