He was born in Gosport, Hampshire, to David (a doctor) and Thelma, with a twin sister Julia. He attended Alverstoke Church of England Primary School and Portsmouth Grammar School, becoming Head Boy in 1983/84. It was whilst playing football with a local team ( RPFC ) that he began demonstrating his prowess as a runner, scoring numerous goals as a flying forward leaving many defenders in his wake. He then joined athletics clubs, re-took one of his A-level exams and began studying medicine at the University of Southampton, but he left his course after three months as he had begun to achieve success as an athlete.
He set the national 400 metre record of 44.37 seconds on 3 July 1996 in Lausanne, Switzerland but that was subsequently broken a year later by Iwan Thomas who shaved 0.01s from Black's time. Fellow GB athlete Mark Richardson also equalled Black's mark in 1998. Black's time stands as the second fastest of all time recorded by a British runner. Black was also part of the British 4 x 400 relay team which upset the strong favourites USA to win the gold medal in the 1991 World Championships in Tokyo.
Black came second in the individual 400m in Tokyo to Antonio Pettigrew. Pettigrew later admitted the use of performance enhancing drugs from 1997 onwards in June 2008. No clear evidence has emerged - and Pettigrew never admitted anything further before his 2010 suicide - using performance enhancing drugs during the 1991 season.
His greatest individual achievement in track and field was in the 1996 Olympics in Atlanta when in the final of the 400m he finished in second place behind Michael Johnson, winning the silver medal in the process. However, partly due to injuries, he never rediscovered this form, and subsequently retired from the sport only two years later in 1998 after he was not selected for the 1998 European Championships.
Black was coached by Mike Smith and Mike Whittingham, and was sponsored by Reebok.
The World Championships' 4x400m originally saw the USA beat Great Britain by 0.18 seconds in a thrilling finale. Subsequently, US athlete, Antonio Pettigrew admitted to using performance enhancing substances during this period.
On 7 January 2010, it was announced that Great Britain's 1997 World Championship 4x400m relay team are to be awarded the gold medal due to the disqualification of the USA team.