He umpired at tennis including
Wimbledon from 1973 to 1984, notably the
men's singles final at Wimbledon in 1984, won by
John McEnroe against
Jimmy Connors. On the verge of becoming one of the tour's first paid international umpires, Mercer moved into tennis commentary for BBC radio in 1985, commentating on the French Open and Wimbledon alongside Tony Adamson on
BBC Radio 2, and became known for his humorous tone. After commentating on the
1992 Wimbledon Championships and
Olympics for BBC Radio, Mercer moved across to BBC Television in the aftermath of the retirement of veteran TV tennis commentator
Dan Maskell, making his BBC TV tennis debut at the
1992 US Open. Mercer became one of the most prominent voices of tennis on British television for the next 28 years, including commentating on the Wimbledon men's singles finals in 1999 and 2000 on BBC television. 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 also commentated for
BT Sport in the 2010s. He was the only person to have both umpired and commentated on a Wimbledon men's singles final, covering 35 Wimbledon tournaments as a broadcaster in addition to his 12 as an umpire. The 2019 edition turned out to be his last. He was due to work once more on the 2020 tournament, but it was cancelled due to the
COVID-19 pandemic. ==Other sports commentary==