[4] In his early career, Williams was a talented sprinter, later becoming a member of the Wales rugby team that won the Five Nations Championship in 1975, 1976, 1978 and 1979, including Grand Slam wins in 1976 and 1978.

He received his initial education at Nantyffyllon Primary and Junior School where he was introduced to rugby by his teacher Eifion Williams.

Under the guidance of his rugby master David Brown, in the sixth form he won a Welsh Secondary Schools’ cap at outside half.

He played a major role in the 1974 'invincible' series against South Africa, scoring two tries in each of the second and third tests (in so doing becoming the first British and Irish Lion to score two tries in the same test match in the 20th Century), and earning the title "The Welsh Whippet",[7] and a last-gasp try against Orange Free State to help preserve the Lions' unbeaten record.

Towards the end of his rugby playing career, in 1980 Williams participated in the hugely popular BBC TV Superstars competition.

Reaching the final, he competed alongside an array of sports stars including 400-metre runner John Sherwood; football World Cup winner Sir Geoff Hurst; top basketball player Steve Assinder; champion boxer Alan Minter; modern pentathlete Danny Nightingale; Olympic gold medalist Daley Thompson and judo legend Brian Jacks.