He immersed himself in the local jazz & blues scene dominated by the likes of John Lee Hooker, Joe Williams, Sonny Terry and Brownie McGhee, Lenny Breau, Oscar Peterson, and Moe Koffman. Clayton-Thomas made his mark more forcibly with his next band, The Bossmen, one of the first rock bands anywhere to include jazz musicians. In 1966 he wrote and performed the R&B-driven anti-war song "Brainwashed", which became a major Canadian hit, peaking at No. 11 on the national RPM chart. One night in 1966 after "sitting in" with blues singer John Lee Hooker in Yorkville, Clayton-Thomas left with him for New York. They played a Greenwich Village club for a couple of weeks; Hooker then left for Europe and Clayton-Thomas stayed on in New York City. He survived by playing "basket houses", where performers were given a few minutes of stage time and then passed the basket. Folk singer Judy Collins heard Clayton-Thomas one night at a club uptown and told her friend, drummer Bobby Colomby, about him. Bobby's band, Blood Sweat & Tears, had broken up four months after releasing its debut Columbia album, "Child Is Father to the Man". Colomby was impressed with Clayton-Thomas's vocal talent and he invited him to join the band. They took the reformed group into the Cafe Au Go-Go in the Village. In his 1974 autobiography, "Clive: Inside the Record Business", Clive Davis, then president of Columbia Records, described his initial impression of Clayton-Thomas singing at the Café Au Go-Go: "He was staggering... a powerfully built singer who exuded an enormous earthy confidence. He jumped right out at you. I went with a small group of people, and we were electrified. He seemed so genuine, so in command of the lyric... a perfect combination of fire and emotion to go with the band’s somewhat cerebral appeal. I knew he would be a strong, strong figure." BS&T continued with a string of hit albums, including "Blood, Sweat & Tears 3" which featured Clayton-Thomas's "Lucretia MacEvil" and Carole King's "Hi-De-Ho," and "BS&T 4", which yielded another Clayton-Thomas-penned hit single, "Go Down Gamblin'." "Blood Sweat & Tears' Greatest Hits" album has to date reportedly chalked up over seven million copies in worldwide sales.