Levy's best singles ranking was # 30 in the world in 2001, and his best doubles ranking was # 76 on July 9, 2007.
Levy began playing tennis at age seven. His family moved to Portugal for a year and half when he was nine years old. They returned to Israel, and in 1992 the family moved to Ramat Hasharon so Harel could train at the tennis center there.
That year, he was # 1 in the under-14 age group in Israel.
After turning pro in 1995, Levy served his required time in the Israeli military, but the IDF (Israeli Defense Forces) allowed him to compete in events during his service.
In March 1998 he and Lior Mor won in Israel, defeating Barry Cowan and Filippo Veglio 6–4, 7–6 in the final. In June he and partner Raviv Weidenfeld won in Ireland, defeating Daniele Braccoalo and Igor Gaudi 7–6, 6–4 in the final. In July he and Lior Mor won in Greece, defeating Gilles Elseneer and Wim Neefs 6–3, 0–6, 6–3 in the final.
In January 2000 he and partner Jonathan Erlich won at Orlando, Florida, defeating Oscar Ortiz and Jimy Szymanski 6–3, 6–4 in the final. In July they won at Newport, Rhode Island, defeating Kyle Spencer and Mitch Sprengelmeyer 7–6(2), 7–5 in the finals.
In July 2000 at Toronto, while ranked only 144th in the world, he beat world # 73 Martin Damm, # 47 Stefan Koubek, # 27 Sebastian Grosjean, # 61 Jerome Golmard, and # 55 Jiri Novak, before losing in the finals to # 9 Marat Safin.
In March 2001 he upset world # 10 Tim Henman of Great Britain 6–2, 6–4 at Scottsdale.
In May 2001 Levy upset the world's top player, his idol Pete Sampras, at the Italian Open. Levy stunned Sampras 7–5, 2–6, 6–4, saving 13 of 17 break points, in what was his most impressive victory yet. In his next match at the tournament, he beat world # 33 Francisco Clavet 6–4, 7–6(6), and then whipped Nicolas Kiefer, 6–2, 6–4, winning 80% of his first serves, to advance to the quarterfinals, where he subsequently lost to Sweden's Andreas Vinciguerra.
In June 2001 Levy upset world # 17 Wayne Ferreira of South Africa 6–2, 6–4, and world # 40 Andy Roddick 7–6(3), 5–7, 6–3, before losing in the finals of the Nottingham Tournament in England to Thomas Johansson of Sweden, 7–5, 6–3.
At the US Open in 2002 he defeated world # 30 Andrei Pavel 1–6, 7–6(7), 4–6, 6–3, 6–4.
Levy was hampered by injuries for much of the 2002 season.
At the qualifying tournament for Wimbledon in 2003, Levy defeated Paul Goldstein in the first round, and reached the 3rd round before losing. In September 2003, Levy and partner Paul Baccanello of Australia won the doubles title at the Open de l'Isere, defeating Rik de Voest and Johan Landsberg 5–7, 6–4, 7–6(5) in Grenoble, France. Levy also reached the singles final at the tournament. Later that month he paired with Amir Hadad to defeat Fred Hemmes and Raemon Sluiter 6–4, 6–4 to win in Groningen, Holland. In October he and Hadad defeated Scott Humphries and Mark Merklein 6–4, 6–7(3), 6–3 to win in Nottingham, England. Levy was back in peak form at the Dnepropetrovsk tournament in November 2003. He reached the singles final before succumbing to Georgian Irakli Labadze 3–6, 6–3, 1–6. Levy fared better in the doubles tournament where, along with partner Jonathan Erlich he won the title in straight sets, 6–4, 6–3, over Simon Aspelin and Johan Landsberg. He and Erlich also won that month at Bratislava, Slovakia, defeating Mario Ančić and Martin García 7–6(7), 6–3 in the final.
The doubles performances of Levy and his partner Amir Hadad in the months of April and May, 2005, were impressive. In late April the Israelis captured the Hungary F1 tournament in Budapest, defeating Nikola Martinović and Josko Topic 5–7, 6–2, 6–1 in the final. A few days later they won the F2 title in Miskolc as well, beating Bastian Knittel and Marius Zay 6–1, 6–0 in the final. Levy and Hadad then competed in May in the German town of Furth, where they took the title from Jan Frode Andersen and Johan Landsberg, 6–1, 6–2. In July they won at Budaors, Hungary, defeating Adam Chadaj and Stephane Robert 6–4, 6–7(7), 6–3.
In 2005 he won the USTA Tulsa Challenger, beating Benedikt Dorsch of Germany, the reigning NCAA men’s singles champion, in a three-hour duel 5–7, 7–5, 7–6 (6). In September 2005 he and partner Noam Okun won in Istanbul, Turkey, defeating David Skoch and Martin Štěpánek in the final, 6-44, 7–5.
In January 2006, a right shoulder injury forced him to retire from a Sydney ATP singles match, and sidelined him for a week. In June 2006 he and Giorgio Galimberti won in Milan, Italy, defeating Frederico Gil and Juan Albert Viloca in the final, 6–3, 6–3. In August he and partner Sam Warburg won in the Bronx, New York, defeating Scott Lipsky and David Martin in the final, 6–4, 7–5.
In April 2007 he and Warburg won at Valencia, California, defeating Cecil Mamiit and Eric Taino in the final, 6–2, 6–4. In June they won at Yuba City, California, defeating Eric Nunez and Jean-Julien Rojer in the final, 6–4, 6–4.
In July 2007 Levy and Rajeev Ram competed together in doubles at Wimbledon, where they made it through the qualifying rounds and to the quarterfinals -- Levy's best grand slam showing to date. On their way they defeated 15th-ranked Martin Garcia and Sebastian Prieto 7–6 (0), 6–7 (4), 7–6 (4), 6–7 (3), 10-8 in the third round. They lost in the quarters to No. 10 seeds Arnaud Clement and Michael Llodra, 6–3, 6–2, 6–2.
Later in July, Levy won a challenger title in Manchester, Great Britain, beating Travis Rettenmaier 6–2 6–4 in the final.
Levy suffered from an injury and hip surgery during his peak years, and has so far not recovered enough to play at his top level.