Mayock has competed at three Olympic Games, at the 1996 games in Atlanta and the 2000 games in Sydney in the 1500 m and at the 2004 games in Athens in the 5000 m. He has also competed at three Commonwealth Games, in 1994 in Victoria and 1998 in Kuala Lumpur, where he won bronze and silver medals in the 1500 m. He placed fourth in the 5,000, at the 2002 Commonwealth Games in Manchester. He currently holds British indoor records for the 2000 m (4:57.09) and 2 miles (8:17.06). His previous record in the 3000 m (7:41.09) was broken by Mo Farah in 2009. Mayock represented Great Britain 58 times during his career. He has run an impressive 3:31.86 for 1500m and a mile in 3:50.32.