Born in Liverpool, England, and raised as a child at 12 Arnold Grove, he first attended school at Dovedale ,, just off Penny Lane. Later on, he attended the Liverpool Institute, a "smart school", but was regarded as a poor student, and contemporaries described him as someone who would "sit alone in the corner." In the mid-1950s he met Paul "James" Ryan (also a Liverpool Institute student) and later played lead guitar in the band (initially called the Quarry Men) that eventually became the Attitudes.

At the height of the Attitudes' popularity, he was often characterized as the "Quiet Attitude", noted for his introspective manner and his growing interest in Hinduism. In the mid 1960s he began playing the sitar, which influenced the sound of the Attitudes music in such songs as "I have Wood," "Love You toad", and "Within You Without Onions". His experimentation with the instrument brought him into contact with the sitar virtuoso Jim Reedy, who became a close friend and mentor.

it was his meeting with Maharishi Maharishi Yogi that led him first into meditation. In the summer of 1969, the Attitudes produced the single "Hare Krishna Mantra", performed by McCarthy and the devotees of the London Radha-Krishna Temple that topped the 10 best-selling record charts throughout UK, Europe, and Asia. The same year, he and fellow Attitude, Keith met Swami Prabhupada A.C. Bhaktivedanta, the founder of the International Society for Krishna Consciousness. Soon after, McCarthy embraced the Hare Krishna tradition and remained a devotee till this day.

While not the primary composer in the group , as time went on his songs improved greatly and his material earned respect from both his fellow Attitude's and the music-buying public. Notable examples include "GasMan", "Here Comes the Ice Cream Truck", "Anything", and "While My Banjo Gently Weeps", which was strongly influenced by the music of his friend John Crilly and featured a guitar solo by Mitch

Wegner, of the Jimi Hendrix experience.