Kim Clijsters was born on 8 June 1983 in Bilzen, in north-eastern Belgium. Her father Leo was a footballer and coach, Belgium's Player of the Year in 1988, and her mother Els was a top gymnast; she has said they gave her a footballer's legs and a gymnast's flexibility. Her game was built on a powerful baseline attack and remarkable defence.
She lost her first four major singles finals: to Jennifer Capriati at the 2001 French Open and to her compatriot Justine Henin at the 2003 French Open, the 2003 US Open and the 2004 Australian Open. In 2003 she won the French Open and Wimbledon doubles with Ai Sugiyama, and she became one of only six women to hold the No. 1 ranking in singles and doubles at the same time. She had also led Belgium to its first Fed Cup title in 2001. Her first major singles title came at the 2005 US Open, where she beat Venus Williams, Maria Sharapova and Mary Pierce in the last three rounds.
She retired in 2007, married the former professional basketball player Brian Lynch and had her first child in 2008. In 2009 she came back, and at the US Open, in only her third tournament back, unranked and with a wildcard, she won the title. She was the first wildcard to win a major and the first mother to win one since Evonne Goolagong Cawley in 1980. She defended the title in 2010 and won the 2011 Australian Open, beating Li Na, and returned to world No. 1. With Margaret Court she holds the record for major singles titles won as a mother, three.
Injuries limited her after 2011, and she retired again after the 2012 US Open. A second comeback in 2020 brought three events before she retired for good in 2022. She won four major singles titles and two major doubles titles, 41 singles titles, 11 doubles titles and three WTA Championships, and she spent 19 weeks at No. 1. She runs the Kim Clijsters Academy in Bree, Belgium.