 Born one of ten children in Stepney, London to a costermonger father, McCarthy was a boyhood friend of Terry Lawless, and had a successful amateur career fighting out of St. George's Gym in Stepney, winning 83 of 90 fights and representing England four times.He turned professional under managers Jarvis Astaire and Ben Schmidt, and made his pro debut in April 1951 with a first round knockout of Hector Macrow.He was unbeaten in his first 28 fights, which included wins over Freddie King, Jackie Turpin, Ronnie Clayton, and Jim Kenny.