She is known for her mental toughness and her one-handed backhand, a stroke which John McEnroe has called the best backhand by any player, male or female.   As of June 2006, she has won five Grand Slam titles, including three at the French Open, as well as the 2004 Olympic Gold Medal.
Since Belgian law does not require a woman to take on her husband's name after marriage, her maiden name—Justine Henin—is still official.
She married tennis coach Pierre-Yves Hardenne on November 16, 2002, in the Château de Lavaux-Sainte-Anne. From then on, she uses the name Justine Henin-Hardenne on the tennis court.
Her mother, Françoise Rosière, was a French and History teacher. She used to take the young Henin-Hardenne across the border to watch the French Open. Her mother died of intestinal cancer when Henin-Hardenne was only 12.
Henin-Hardenne, known as "Juju" to many of her fans, has been coached by Carlos Rodriguez of Argentina since she was 14. She regularly reached late rounds of international competitions, and won five ITF tournaments by the end of 1998.
She started her professional career in the WTA tour in May 1999 as a wildcard entry in the Belgian Open at Antwerp, and became the fifth player to win her debut WTA Tour event.
Henin-Hardenne established herself as a major competitor in 2001. She reached the semifinals of the French Open and the final of Wimbledon. By the end of the year, Henin-Hardenne was ranked number seven in the world, with three titles to her name.
In 2002, she reached four WTA finals, winning two of them. Henin-Hardenne finished the year as the world number five. Her German Open victory, her first win at a Tier I tournament was noteworthy, as she beat then world number two Jennifer Capriati in the semi-final, and then world number five Serena Williams in the final.
2003 was the year of Henin-Hardenne in the WTA tour. On June 7, she won her first Grand Slam tournament, the French Open, defeating her Flemish compatriot Kim Clijsters in the finals, 6-0 6-4. On September 7, she won her second major tournament, the US Open, beating Clijsters again in the finals, 7-5 6-1. In both tournaments, her straight sets finals victories contrasted well against her semi-finals matches (see Famous matches section). Henin-Hardenne needed three sets to defeat Serena Williams in a controversial win in the French Open. In the US Open, she reached the final by beating Jennifer Capriati, winning 7-6 in the final set; in the match, she was two points away from defeat in no less than 11 times. On October 19, Henin-Hardenne gained the number one ranking on the WTA list, taking over from Clijsters. She was named the International Tennis Federation's women's singles World Champion for 2003.
She started her 2004 season by winning a warm-up tournament in Sydney, before going on to clinch her third Grand Slam title at the Australian Open on January 31. She once again defeated Clijsters in a three-set final, 6-3 4-6 6-3. On March 22, Henin-Hardenne accumulated the highest point total (7,626) in the history of the WTA rankings. Since the awarding of quality points was eliminated in 2006, and it is not possible to surpass Henin-Hardenne's record point total without the benefit of scoring any quality points, this is a tour record that may never be broken. By the end of the 2004 spring hard court season, she had already built a 25-match Tier I winning streak and a 22-1 win-loss record (winning her first 16 matches).
By the start of the 2004 clay court season, her health was affected by a strain of cytomegalovirus. This was further complicated by an immunity problem. She often slept up to 18 hours a day and barely had the strength to brush her teeth, let alone play competitive tennis.
Although she decided to defend her French Open title and was seeded first in the tournament, her health was still not up to the task. Henin-Hardenne lost her second round match against a much lower-ranked player Tathiana Garbin of Italy. At the time, the loss marked only the second time in 15 Grand Slam events that Henin-Hardenne exited before the fourth round.
She came back in August, somehow finding the strength to win the gold medal at the Summer Olympics in Athens, Greece, defeating Amélie Mauresmo of France in the final, 6-3 6-3. On the way to the gold, Henin-Hardenne rallied for a miraculous win against Anastasia Myskina of Russia in the semi-final (see Famous matches section). In September, she attempted to defend her US Open title. However, she lost to Russian Nadia Petrova in the fourth round. As a result, she lost the number one ranking that she had held for 45 non-consecutive weeks. She then withdrew from the remaining tournaments of the season to recuperate from the infection. Overall, Henin-Hardenne withdrew from a total of 10 tournaments in 2004.
Her plan to rejoin the tour in the beginning of 2005 was delayed when she fractured her kneecap in a training session in December 2004.
On March 25, 2005, after more than six months of inactivity, Henin-Hardenne returned to the WTA circuit at the NASDAQ-100 Open in Miami. She lost a hardcourt match to new Russian star and then world no. 2 Maria Sharapova in the quarter-final. She rebounded at her next tournament, winning the Family Circle Cup at Charleston. She went on to win two further clay court titles by the start of the 2005 French Open. Her victories over then world number one Lindsay Davenport, Russians Sharapova, Elena Dementieva, Svetlana Kuznetsova and Nadia Petrova made her the top contender for the Grand Slam title.
Henin-Hardenne was seeded 10th in the French Open, and went on to defeat the French player Mary Pierce, 6-1 6-1, to take her second title at Roland Garros. The win marked Henin-Hardenne's 24th consecutive clay court win and her 10th consecutive final win, a streak stretching back to Zurich in October 2003. In capturing the title, Justine managed a fourth round comeback win over Kuznetsova (see Famous matches section). She also demolished Maria Sharapova in the quarter-final, and Petrova in the semi-final.
With her French Open victory, Henin-Hardenne moved from number 12 to number seven in the world rankings. She joined Monica Seles as the only two currently active players on the WTA Tour to have won the French Open at least twice, and is a perfect 24-0 in her 2005 clay court campaign.
At Wimbledon 2005 Henin-Hardenne's winning streak of 24 matches was snapped in the first round by Greek Eleni Daniilidou, 6-7, 6-2, 5-7. With this defeat she became the first French Open champion in the Open Era to lose in the opening round of Wimbledon. A hamstring injury sustained earlier in the year eventually limited Henin-Hardenne to 11 matches since she captured her second Roland Garros title.
In 2005, TENNIS Magazine put her in 31st place in its list of 40 Greatest Players of the TENNIS era. In November, at the 2005 Sony Ericsson WTA Tour Championships, she was named the inaugural winner of the Whirlpool 6th Sense Player of the Year which honors the player who has demonstrated the most 6th sense intuition, that is to say heightened intelligence, unbeatable performance and pinpoint precision.
In January 2006, Henin-Hardenne returned to competitive tennis in a tournament in Sydney, a tune-up for the 2006 Australian Open. She was seeded fifth and drew former world number one Martina Hingis in a much-hyped first round match. Henin-Hardenne overpowered her opponent in straight sets, 6-3 6-3. Finding excellent form, she routed former US Open champion Kuznetsova in the semi-final, 6-3 6-1, before defeating Francesca Schiavone in the final, 4-6 7-5 7-5.
In her Australian Open campaign, Henin-Hardenne beat reigning world number one Davenport and fourth ranked Sharapova in three-set matches to set up a final match against Frenchwoman Amélie Mauresmo, the world number three. While trailing 1-6 0-2, she retired from the match. Henin-Hardenne's decision to give up, citing a stomach pain, was greeted with controversy, as she became only the second player, and the first woman, to retire from a Grand Slam final in the Open Era.
Henin-Hardenne captured her second title of 2006 in February, defeating Sharapova, 7-5 6-2 in a Tier II event in Dubai. This was her third Dubai title, having won in 2003 and 2004.
In the following Pacific Life Open Tier I tournament in Indian Wells, Henin-Hardenne lost a hard-fought semifinal match to fourth seed Dementieva, 6-2 5-7 5-7. She was also ousted easily from the Miami NASDAQ-100 Open in the second round by Meghann Shaughnessy, 7-5 6-4. In April, Henin-Hardenne failed in her attempt to defend her title at the Charleston Family Circle Cup as she played at her first clay court event of the season. She lost to third-seeded Patty Schnyder, 6-2 3-6 2-6 in the semi-final. It was her first defeat in the Tier I tournament.
However, on April 23 and 24, Henin-Hardenne scored one of the highlights of her career as she led Belgium to victory over defending champion Russia in the Fed Cup. She triumphed over world number five Petrova, 6-7 6-4 6-3, and world number nine Dementieva, 6-2 6-0, helping to send Belgium to the semi-finals. The Fed Cup wins were particularly impressive in that Petrova came into the match with two straight clay court tournament victories and a 10-match winning streak on the surface, while Dementieva beat Henin-Hardenne in their last meeting in Indian Wells and defeated second-ranked Belgian compatriot Clijsters on Day 1 of the tournament.
Henin-Hardenne played at the Tier I event in Berlin as the defending champion and beat reigning world number one Mauresmo, 6-1 6-2 in the semi-finals. However, she lost to Nadia Petrova in the final, 6-4 4-6 5-7.
At the French Open in June 2006, the defending champion was able to rebound from her loss in Berlin. Henin-Hardenne stormed through her semi-final match by dismissing second seed Clijsters, 6-3 6-2 in a relentless display of attacking tennis. She then defeated Kuznetsova in the final, 6-4 6-4 to win her third title in four years at Roland Garros. Henin-Hardenne captured the title without the loss of a set and became the first French Open champion to successfully defend her title since Steffi Graf in 1996.