When Kempson was still attending Queen's College, in Queenstown, he was selected to play in the South Africa Schools side. After school, he joined, where he played his first class rugby until 1998. Kempson was selected to represent South Africa at various youth or development levels; in 1994, he represented the South Africa Under-23 team and later in the same year, he toured with a South Africa Development side to the United Kingdom. He was named on the bench for in a match in 1995 against in Johannesburg, but failed to make an appearance; but his good form continued as he was named the South African Rugby Young Player of the Year for 1995 In 1996, he played for a South Africa 'A' team that toured the United Kingdom and in 1997, he played for both the Sharks and the Emerging Springboks against the British and Irish Lions during their 1997 tour to South Africa. On 20 June 1998, he finally made his test debut, playing off the bench in their match against in a mid-year rugby union international. He was promoted to the starting line-up for their 96–13 victory over a week later and retained the number one jersey in an 18–0 victory over. After the 1998 Currie Cup, Kempson move to Cape Town, where he joined Currie Cup side and Super Rugby side the. However, he failed to be selected in the South Africa side that competed at the 1999 Rugby World Cup, instead joining Welsh side Newport on a short-term basis, here he joined fellow South AfricansGary Teichmann, Franco Smith and Andy Marinos. He returned to South Africa to play for the Stormers and Western Province in 2000 and 2001, also forcing his way back into Springbok selection. However, a neck operation at the start of 2002 ruled him out of the entire 2002 Super 12 season. He then signed a deal with Irish side Ulster, where he joined former Stormers coach Alan Solomons. He did return to South Africa to play Stormers during the 2003 Super 12 season and appeared for the Springboks in the 2003 Tri Nations Series – where South Africa's 9–29 defeat to turned out to be Kempson's final test match for South Africa – before returning to Ulster. When Solomons left Ulster to join English Premiership sideNorthampton Saints, he also lured Kempson across the Irish Sea. However, Kempson's time in Northampton was marred by injuries and he was released after just one season.
Coaching career
Kempson's relationship with Alan Solomons continued when his playing career ended, and Kempson was appointed a forwards coach at the, where Solomons was the technical director. He also assisted Gary Gold by coaching the Vodacom Cup team in 2007 and in their preparation for the 2007 Rugby World Cup. In 2009, Kempson moved to Port Elizabeth to join Solomons' coaching staff at the, where he was also appointed the manager of their newly established academy in 2010. Kempson remained in his role as Academy Director over the next few years, also coaching the side in the 2011, 2012 and 2013 Under-21 Provincial Championships and the in the 2014 and 2015 Varsity CupYoung Guns competitions. In March 2016, the Eastern Province Rugby Union confirmed that Kempson would be the head coach of the for the 2016 Currie Cup qualification series.
