Clark is from a well-known British basketball family, his father Mark coached the GB national women’s team from 2006–09 and his mother played for the National team. His sister Ella Clark is also an international basketball player. Clark decided to reject the chance to play college basketball in the United States and instead opted to accept an invitation to play at the academy of Spanish ACB club, CB Estudiantes. Before this, he attended Chingford Foundation School.
Coming through the Spanish club's junior ranks, Clark made his full debut in the ACB in December 2006 before spending loan spells in the Spanish second division with the Estudiantes farm team CB Breogan in the 2007-08 and 2008-09 seasons. Since the start of the 2009-10 Clark established himself into the regular rotation for CB Estudiantes and then into the starting five.
Clark has represented England and Britain at junior and under-20 levels, He earned his first cap for the British senior team in the summer of 2009 and was part of the team that competed at the 2009 Eurobasket in Poland. Clark also represented Team GB at the 2012 Summer Olympics in London.