Born in Mönchengladbach, North Rhine-Westphalia, Frentzen began karting at the age of twelve after his father bought him his first kart. He won the German Junior Kart Championship in 1981 at age fourteen. His father, Heinrich-Harald Frentzen, who ran a funeral business, acted as both team boss and head mechanic during Frentzen's early career.
Frentzen moved into car racing in 1985 via German Formula Ford 2000, finishing runner-up in that series in 1987. He progressed to German Formula Opel Lotus in 1988 under the guidance of former Formula One driver Jochen Mass, winning the championship in his first season. His teammate Marco Werner finished third in the same standings.
The 1989 German Formula Three Championship proved a pivotal year. Frentzen competed against both Michael Schumacher and Karl Wendlinger in what became a celebrated title battle, with the German motorsport committee (ONS) actively backing both Frentzen and Schumacher as potential Formula One standard-bearers. Wendlinger won the championship; Frentzen and Schumacher finished as joint runners-up on identical points totals.
Frentzen then contested International Formula 3000 in 1990 with Eddie Jordan Racing, partnered by Eddie Irvine, and followed that with racing in Japan across several seasons before earning his Formula One opportunity.
Frentzen made his Formula One debut at the 1994 Brazilian Grand Prix with Peter Sauber's team, partnering Karl Wendlinger in a Mercedes-powered car. He qualified fifth in Brazil and scored early points, including fifth in the Pacific Grand Prix. When Wendlinger was sidelined by serious head injuries sustained during qualifying at Monaco, Frentzen became the de facto team leader and comfortably outpaced substitute teammates Andrea de Cesaris and JJ Lehto for the remainder of the year.
Sauber lost Mercedes engines after 1994 and switched to Ford V8 power. Despite the less competitive machinery, Frentzen drove consistently over two further seasons. His highlight came at the 1995 Italian Grand Prix, where he took Sauber's first podium finish. He matched up well against teammates Wendlinger and later Jean-Christophe Boullion, and his performances were noticed by Williams.
For 1997, Frentzen replaced reigning World Champion Damon Hill at the Williams-Renault team, partnering Jacques Villeneuve. He opened the season strongly, leading the first race before a brake disc failure, and then took his maiden victory at the San Marino Grand Prix. He also claimed his first pole position at Monaco, though he did not finish that race.
After an inconsistent first half of the year, Frentzen strung together six consecutive points-scoring results in the second half of the season, including five podiums. Despite eight front-row starts and seven podiums across the year, he generally sat second to Villeneuve within the team — qualifying alongside the Canadian only four times. Frentzen finished third in the championship with 42 points; following Michael Schumacher's disqualification for his collision with Villeneuve at the final race, Frentzen was elevated to second in the final standings.
The 1998 season brought a decline in Williams competitiveness as Renault ended factory engine support and designer Adrian Newey departed for McLaren. Frentzen managed one podium, at the opening round in Melbourne, and finished seventh in the championship with 17 points. Conflicts with technical director Patrick Head contributed to his departure.
Frentzen moved to Jordan in a straight swap with Ralf Schumacher and produced the finest sustained period of his career. Driving the Mugen-Honda powered Jordan 199, he won at the French and Italian Grands Prix in 1999 and was in genuine championship contention late in the season. During the European Grand Prix he had been on course to potentially draw level with both Häkkinen and Irvine in the standings before his car stopped on lap 32. He ultimately finished third in the World Drivers' Championship with 54 points, widely regarded as the driver of the year.
The 2000 season brought Jordan into conflict with Honda's preference to favour its other customer team, BAR, for engine supply priority. Frentzen managed two podiums but the team fell behind BAR in the pecking order. In 2001, a run of retirements and internal disagreements — reportedly including Frentzen offering to fund car development himself — led to Jordan terminating his contract mid-season. Eight years later Eddie Jordan revealed the dismissal was partly to secure Honda-backed driver Takuma Sato. Frentzen moved to the struggling Prost team, qualifying fourth at Spa before Prost went bankrupt at the end of the season.
Signed by Arrows for 2002, Frentzen scored points twice before the team went bankrupt in August and folded. He returned to Sauber for 2003, having driven a one-off for the team at the 2002 United States Grand Prix replacing Felipe Massa. Evenly matched with highly rated teammate Nick Heidfeld, Frentzen scored a final podium at the 2003 United States Grand Prix before retiring from Formula One at the end of the year.
His Formula One record across a decade: three wins, two pole positions, six fastest laps, and 18 podiums.
Frentzen moved to the DTM in 2004 driving an Opel Vectra. The car was uncompetitive and he finished 14th. He remained with Opel in 2005, improving to eighth overall as the team's best-placed driver, with a podium at Brno from pole position. After Opel withdrew at the end of 2005, Frentzen joined Audi for 2006, finishing third at Hockenheim and Barcelona on his way to seventh in the final standings before departing citing lack of team support.
Frentzen competed in the Speedcar Series in 2007–08 and the full 2008–09 season. He drove at the 2008 24 Hours of Le Mans for Aston Martin Racing in the GT1 class alongside Karl Wendlinger and Andrea Piccini, finishing fourth in class. He also entered a self-built HHF Hybrid Concept Car at the 2008 Nürburgring 24 Hours, though gearbox failures prevented official classification.
In 2011, he won a special Race of Champions Legends race against Hans-Joachim Stuck, Marc Duez, and Stig Blomqvist. He returned to GT racing in the ADAC GT Masters in 2012 and 2014.
Early in his career, Frentzen was in a relationship with Corinna Betsch; she later married Michael Schumacher. Frentzen married Tanja Nigge in 1999 and they have three children.
Frentzen is remembered as a driver whose natural ability was never quite matched by consistent results over a full championship season. His 1999 campaign with Jordan came closest to a title challenge. Team bosses and commentators consistently cited him as one of the most gifted drivers of his era, with Peter Sauber calling him the most important driver in the team's history. His career arcs — from near-obscurity in midfield machinery to championship contention and back — mirror the fortunes of the teams that surrounded him as much as his own performances.