Born in Berlin, Germany, in the spring of 1942, he came of age amid the beat boom that spread across Europe — his interests included art as well as music, and Voormann's first contact with the group predated their final lineup. He was part of Hamburg's bohemian/beat community, and involved romantically with photographer Astrid Kirchherr, who threw him over for Stu Sutcliffe, the Beatles' bassist on their first two visits to the city. Voormann had some musical training, in classical guitar, which was enough to draw him into the city's music scene, which was dominated by the Liverpool bands playing there. In 1964 he joined the Liverpool group the Eyes, succeeding Lewis Collins on bass — an instrument he'd never previously played — and returned with them to Liverpool. Despite their promise, the Eyes only lasted together until the beginning of 1965, but out of that group's collapse, Voormann, drummer Gibson Kemp, and lead guitarist Paddy Chambers chose to continue playing together, in a trio called Paddy, Klaus & Gibson, which quickly fell into the orbit of Beatles manager Brian Epstein.
Despite Epstein's efforts, however, Paddy, Klaus & Gibson never saw any major success. The contact with Epstein, coupled with his continued, now longstanding friendship with Beatles, was sufficient to get Voormann an unexpected and very visible showcase for his skills as an artist — in 1966, he devised the distinctive cover for the Revolver album. The same year that he created the Revolver cover, Voormann also showed just how formidable he'd become on his instrument when he succeeded Jack Bruce — one of the two or three most prominent bassists in England — in the lineup of Manfred Mann. Voormann stayed with the band for nearly three years and played on such hits as "Ha Ha Said the Clown" and "The Mighty Quinn," the latter a number one British hit and a Top Ten single in America in early 1968. That same year, he also designed the cover of the Bee Gees' Idea album. Manfred Mann's final split in the summer of 1969 left Voormann free to pursue other opportunities.