Watson originally played amateur rugby union in England for Dudley Kingswinford in Staffordshire competition before answering a St. Helens club advertisement for "top class Rugby Union forwards". A trial was arranged and in 1960 he was signed to the club for £750 initially and then a further £750 after he had completed six first grade games for the club. However his career first started to gain momentum after the 1961 Rugby League Challenge Cup Final against Wigan; in front of 95,000 fans Watson's defence was instrumental in helping his club gain a 12-6 victory over their rivals and helped keep Cliff a permanent fixture in the team line-up for the next ten years.