Born at Grahamstown, Cape Province, South Africa, in 1956, Clark is the son of Roger and Betty Clark. He was educated at St. Andrew's College, Grahamstown, and Rhodes University, where he graduated BA and HDE, then at Downing College, Cambridge, where he held the Douglas Smith Scholarship and graduated MA in 1981. At Cambridge he was, on occasion, a member of the University's cricket XI. and was president of the Downing College MCR.
Clark taught at Westerford High School, Cape Town, from 1984 to 1990. He then worked at Liberty Life before being appointed as Headmaster of St Joseph's Marist College, Cape Town, in 1992 and of his own old school, St Andrew's College, in 1994. In 2002 he moved as head to Gresham's School in Norfolk, England. Thereafter in 2008, he was appointed at Malvern College in Worcestershire for his fourth headship.
In 1981, Clark married Dr Brigitte Jennifer Lang, and they have one son and two daughters.