He played most sports at school and university, and won the Welsh junior doubles at tennis in 1968.
He became a freelance sports reporter after winning a competition organised by BBC Wales in 1979, for a time combining this work with his legal practice and with public relations duties for the Law Society.
Alongside his legal career, he also stood as the Conservative candidate in the Swansea West parliamentary constituency in 1979.
On the verge of becoming one of the tour’s first paid international umpires,[5] Mercer moved into tennis commentary for BBC radio in 1985, commentating on the French Open and Wimbledon alongside Tony Adamson on BBC Radio 2,[6] and rapidly became known for his humorous tone.
In addition, he also commentated from the early 1990s for Eurosport on their coverage of the Australian, French and US Opens, and weekly WTA tournaments.
He became the BBC's regular badminton commentator at Commonwealth and Olympic Games, starting at Sydney 2000.