Henin, who will turn 26 June 1 said at a news conference in Limelette, Belgium: "I'm at the end of the road. This is the end of a child's dream."
She gave no simple reason for the retirement less than 10 years after turning professional but she withdrew from this week's WTA event in Rome because of fatigue. The announcement comes less than two weeks before the French Open, an event she won each of the last three -- and four out of the last five -- years.
"I started thinking about (retirement) late last year," she said. "I was at the end of the road. I leave with my head held high."
Henin is coming off a hugely successful year in 2007, when she won 10 tournaments, including the French Open and U.S. Open. She has won seven Grand Slam tournaments and 41 titles overall.
She first reached No. 1 in the rankings Oct. 20, 2003. She's held the top spot 61 consecutive weeks and 117 weeks overall.
"Justine Henin will be remembered as one of the all-time great champions in women's tennis, and a woman who made up for her lack of size with a will to win and fighting spirit that was second to none," said women's tennis tour Chief Executive Officer Larry Scott. "It is rare that an athlete leaves at the very top of her game in this day and age, but Justine has always played by her own rules, in the very best sense of those words."