The core of the band formed as The North London Invaders in 1976, and included Mike Barson (Monsieur Barso) on keyboards and vocals, Chris Foreman (Chrissy Boy) on guitar and Lee Thompson (Kix) on saxophone and vocals. They later recruited John Hasler on drums and Cathal Smyth (better known as Chas Smash) on bass guitar. Later in the year, they were joined by lead vocalist Dikron Tulane.
This six-piece line-up lasted until part way through 1977, when Graham McPherson (better known as Suggs) took over the lead vocals after seeing the band perform in a friend's garden. Dikron went on to be an actor under the name Dikran Tulaine. Smyth, who left after an argument with Barson, was replaced by Gavin Rodgers, Barson's girlfriend's brother. McPherson was kicked out of the band for too often choosing to watch Chelsea instead of rehearsing. Thompson left the band after Barson criticised his saxophone playing.
By 1978, the band had allowed McPherson to return, after filling in temporarily for Hasler (who had taken over vocals when McPherson was removed). Thompson returned after patching things up with Barson. Drummer Daniel Woodgate (Woody) and bass player Mark Bedford (Bedders) also joined the band, replacing Garry Dovey and Rodgers, respectively. After briefly changing their name to Morris and the Minors, the band renamed itself as Madness in 1979, paying homage to one of their favourite songs by ska/reggae artist Prince Buster. The band remained a sextet until late 1979, when Chas Smash rejoined and officially became the seventh member of Madness as a backing vocalist and dancer.