John won nine caps for Ireland. Despite facing setbacks, such as a broken leg in 1977, he joined the 1980 British and Irish Lions tour to South Africa, contributing to their sole test victory over the Springboks in the series. Joining Arthur Guinness & Sons after university, he continued to make significant contributions to rugby, captaining the Greystones Club and the Leinster Provincial side to two championship victories.

However, a decision to tour South Africa with Ireland in 1981 resulted in John losing his job, prompting him to emigrate and eventually become a South African citizen after the democratic elections in 1994. He played rugby for Wanderers, winning 83 caps for the Transvaal side. He also played in two Currie Cup and two Lion Cup Finals. He sat on the bench for the Springboks four times and played for them on the internal tour in 1985. However, no caps were awarded for this. John was voted one of the five SA players of the year in 1987 and he retired from rugby the following year. He also won the SA Superstars title for multiple sports and athletic performances.

In 1986, John joined 702 as a sports reporter, earning recognition as the 'SA Sports Journalist of the Year' twice, once for radio and once for television. His career expanded into current affairs, hosting notable radio shows like "Talk at Ten" and "The Breakfast Show" for seventeen years, during which he won ‘Best Morning Host’ and ‘Best Morning Show’ on multiple occasions and achieved significant audience and revenue growth.

For a spell, he co-hosted with Dan Moyane, in what was then, the first multi-racial breakfast show in SA. They were known as “The Cereal Killers”!

Over the years John has interviewed almost all the top decision-makers in South Africa, building a reputation for professionalism, integrity and fairness. Archbishop Desmond Tutu told him that his show was not a radio show, but rather ‘a mission’. Nelson Mandela once told John to “shut up!” but this was followed with a hearty laugh. Eugene de Kock, the apartheid assassin, revealed that he had once been instructed to kill John because of the influence of his show. John was one of the very first people publicly to call out a government minister over the insane Aids policies of the time and it led to the ANC demanding that he be fired. He wasn’t!

John received a rare Lifetime Achievement radio award for his thirty-year tenure at 702. He is an Ambassador for the Laureus Sport for Good Foundation, a Rotary Paul Harris fellow, and for his work with Reach for a Dream Foundation, he had a star in the constellation of Perseus named after him.

Post-retirement, John remains active, engaging in several business ventures and entertainment pursuits, including appearances in Janice Honeyman's iconic Christmas pantomime, involving 72 shows in two months, and performing a stand-up comedy routine at Joe Parker's Comedy Club.

Most recently John has hosted a television series on the a History Channel that has led to a planned second edition.