Before the Clash's founding, the band's future members were active in different parts of the London music scene.
John Graham Mellor sang and played rhythm guitar in the pub rock act The 101ers, which formed in 1974. By the time the Clash came together two years later, he had already abandoned his original stage name, "Woody" Mellor, in favour of "Joe Strummer", a reference to his rudimentary strumming skills on the ukulele as a busker in the London Underground.
Mick Jones played guitar in protopunk band London SS, which rehearsed for much of 1975 without ever playing a live show and recording only a single demo. London SS were managed by Bernard Rhodes, a sometime associate of impresario Malcolm McLaren and a friend of the members of the McLaren-managed band, the Sex Pistols. Jones and his bandmates became friendly with Sex Pistols Glen Matlock and Steve Jones, who would assist them as they tried out potential new members. Among those who auditioned for London SS without making the cut were Paul Simonon, who tried out as a vocalist, and drummer Terry Chimes. Nicky Headon drummed with the band for a week, then quit.
After London SS broke up in early 1976, Rhodes continued as Jones's manager. In February, Jones saw the Sex Pistols perform for the first time: "You knew straight away that was it, and this was what it was going to be like from now on. It was a new scene, new values—so different from what had happened before. A bit dangerous." At the instigation of Rhodes, Jones contacted Simonon in March, suggesting he learn an instrument so he could join the new band Jones was organising. Soon Jones, Simonon on bass, Keith Leveneon guitar and "whoever we could find really to play the drums" were rehearsing. Chimes was asked to audition for the new band and got the job, although he soon quit.
The band was still searching for a lead singer. Chimes recalls one Billy Watts (who "seemed to be, like, nineteen or eighteen then, as we all were") handling the duties for a time.Rhodes had his eye on Strummer, with whom he made exploratory contact. Jones and Levene had both seen him perform and were impressed as well. Strummer, for his part, was primed to make the switch. In April, he had taken in the opening act for one of his band's gigs—the Sex Pistols. Strummer later explained:
I knew something was up, so I went out in the crowd which was fairly sparse. And I saw the future—with a snotty handkerchief—right in front of me. It was immediately clear. Pub rock was, "Hello, you bunch of drunks, I'm gonna play these boogies and I hope you like them." The Pistols came out that Tuesday evening and their attitude was, "Here's our tunes, and we couldn't give a flying fuck whether you like them or not. In fact, we're gonna play them even if you fucking hate them."
On 30 May, Rhodes and Levene met surreptitiously with Strummer after a 101'ers gig. Strummer was invited to meet up at the band's rehearsal location on Davis Road. After Strummer turned up, Levene grabbed his guitar, stood several inches away from Strummer, looked him in the eye and then began playing "Keys to Your Heart", one of Strummer's own tunes.
Rhodes gave him 48 hours to decide whether he wanted to join the new band that would "rival the Pistols." Within 24 hours, Strummer agreed. Simonon later remarked, "Once we had Joe on board it all started to come together." Strummer introduced the band to his old school friend Pablo LaBritain, who sat in on drums during Strummer's first few rehearsals with the group. LaBritain's stint with the band did not last long (he subsequently joined 999), and Terry Chimes—whom Jones later referred to as "one of the best drummers" in their circle—became the band's regular drummer.
In Westway to the World, Jones also says, "I don't think Terry was officially hired or anything. He had just been playing with us." Chimes did not take to Strummer at first: "He was like twenty-two or twenty-three or something that seemed 'old' to me then. And he had these retro clothes and this croaky voice". Simonon came up with the band's name after they had briefly dubbed themselves the Weak Heartdrops and the Psychotic Negatives. He later explained the name's origin: "It really came to my head when I started reading the newspapers and a word that kept recurring was the word 'clash', so I thought 'the Clash, what about that,' to the others. And they and Bernard, they went for it."