Named after Britain’s emergency telephone number, 999 was founded in London by singer/guitarist Nick Cash and Guy Days. Cash and Days met each other when the former was a member of the pub rock band Kilburn and the High-Roads, and the latter was a session guitarist who played on some of the band’s demo tapes

999 soon established themselves as a powerful live act on London's punk scene and became regulars at the Hope and Anchor, Islington. On the strength of their well received, self-financed debut single, 999 were signed to United Artists Records around the same time as the Buzzcocks. 'I'm Alive' became a firm favourite in the punk clubs. The band's second single 'Nasty Nasty' was cited nearly 20 years after its release as a seminal punk single.

Their self-titled debut album, produced by Andy Arthurs, was released in March 1978, and reached No. 53 in the UK Albums Chart. The following year, the song 'Emergency' from the album appeared — alongside songs by bands like The Jam and The Stranglers — on the punk compilation '20 of Another Kind'. That album reached No. 45 in the UK chart. Years later 'Emergency' was included in Mojo magazine's list of the best punk rock singles of all time.

The band's second album 'Separates' was produced by Martin Rushent and included the classic 'Homicide'. One reviewer lists it as one of the best punk albums of all time.

As a result of extensive touring in the United States in the early 1980s, the band's third and fourth studio albums: 'The Biggest Prize in Sport' and 'Concrete', each charted on the U.S. Billboard 200.

Despite having formed in 1976, 999 have only experienced two permanent changes to their original lineup and have continued to record and play live to the present day, leading Allmusic to describe the band as "one of the longest-lived groups of the punk era."