Frentzen was born in the West German city of Mönchengladbach to a German father and a Spanish mother. After 5 years in karting, at the age of 18 Frentzen entered the German Formula Ford 2000 series, in 1986. As in his karting career, he was funded and supported by his father (a funeral director) who also acted as both team boss and head mechanic. After two seasons in Formula Ford he was runner-up in the 1987 series, despite not participating in all races.
Frentzen progressed to German Formula Opel Lotus in 1988 in the Junior Team of former Formula One driver Jochen Mass, who had been impressed by Frentzen's performances in Formula Ford. Frentzen was champion of the German series in his first year, as well as participating in the Formula Opel Lotus Euroseries (in which he finished 6th). The next step was the German Formula 3 Championship in 1989, where Frentzen competed against many future stars including Michael Schumacher and Karl Wendlinger. At the time, there was a big push by Bernie Ecclestone to have a German driver in the Formula One World Championship, so the ONS (the German National Motorsports committee) decided to support both Frentzen and Schumacher. The ONS put up the reward of a Formula One test to the driver who first would take a victory in a Formula 3 race. This ultimately ended up being Schumacher, in a controversial race at Zeltweg, Austria in which Frentzen claimed Schumacher had forced him off the track. However, Schumacher did not get the Formula One test drive anyway; Karl Wendlinger won the German Formula 3 Championship and Frentzen became joint runner-up with Schumacher (the two finishing on identical points totals).
In 1989 HHF got a contract to drive for Mercedes-Benz with Michael Schumacher and Karl Wendlinger. They were probably the three most talented German drivers and they got a chance to prove it in the Group C Sportscar Championship with Sauber-Mercedes. The experienced drivers like Jochen Mass, Mauro Baldi and Jean-Louis Schlesser were the driving instructors for the three 'young guns'. Frentzen was the quickest of the three and always had better fuel consumption and less tyre wear than Schumacher and Wendlinger. This led to the accolade of being quicker than Schumacher. After finishing second at Donington with Jochen Mass he went to Formula 3000 the next year. He thought this would be the right way to Formula One.
Frentzen did not believe that he could afford to wait for Mercedes' eventual graduation to F1, however, and for 1991 he turned his back on sportscars to drive full-time for Eddie Jordan in F3000.
After promising winter testing when he was the quickest of the 33 drivers the rest of the season was a disaster and HHF rarely saw the finish line. This disastrous decision that left only Japanese F3000 open to him for 1992. To make matters worse, Schumacher had made his sensational debut with Jordan in F1 at Spa in 1991, and was now racing for Benetton. It is a measure of Frentzen's candor that he blamed no-one but himself for the downturn in his fortunes.
In 1994 Frentzen was given a Formula 1 drive by Peter Sauber in a Mercedes powered car, as team mate to Wendlinger. So impressive was he that Frank Williams asked him to replace Ayrton Senna at Williams after the Brazilian's death, but Frentzen chose to remain with Sauber and his performances helped to maintain the team's momentum after Karl Wendlinger was seriously injured at Monaco. The following year in the now Ford-powered Sauber he got his first podium finish and ended the year 9th in the Drivers Championship. However, the 1996 Sauber was unreliable, with many races ending in retirements and Frentzen dropping down the order, though he was one of only four drivers remaining at the end of that year's chaotic, rain-soaked Monaco Grand Prix.
1997 should have been Frentzen's breakthrough year as he was signed to the dominant Williams-Renault team . He scored his first win at San Marino but the season was disappointing; after the family-atmosphere at Sauber Frentzen found life at Williams difficult, in particular having a troubled relationship with Patrick Head. Despite qualifying for many races on the front row he had a tendency to drift back in the race, usually finishing well behind team mate Jacques Villeneuve. The next year Williams lost the Renault engine and were squeezed out by the more competitive Ferrari and Mclaren teams, with Frentzen's best result a third in the first race of the season.
After an unhappy 1998 he was preparing to return to Sauber, his chance at a top drive apparently over, when Jordan stepped in with a timely offer of a straight swap with Ralf Schumacher. It was precisely what Frentzen needed. Backed by a team that he felt believed in him, he rebuilt his career and his morale with a series of drives that left Hill in the position he himself had been in the previous year. Only a blocked air filter prevented him winning the Australian GP, but he went on to take a well-judged win in France and another in Italy to silence his critics. A string of other good results left him third in the World Championship behind Hakkinen and Irvine. He was regarded by many as the driver of the year and a strong contender for the 2000 title.
2000 and 2001 were critical years as Honda also began to supply the BAR team, resulting in a race between the teams as to who would secure the regular engine supply. In 2000 Frentzen managed two podiums, the best results for the team, but Jordan still finished down the grid and, crucially, behind BAR. After some low points finishes, injury, disagreements about the technical direction of the team (Frentzen reportedly offered to pay for the changes to fix the car, out of his own pocket) and then a string of retirements half way through the 2001 season, Jordan dropped Frentzen and replaced him with Jean Alesi. Frentzen took legal action and while waiting for the case to come to court signed to drive for Tom WalkinshawÍs Arrows team in 2002. For the remained of 2001, Frentzen took Alesi's place at the struggling Prost team, and managed to qualify a brilliant 4th at Spa, before the outfit collapsed at the end of the season.
2002 produced some promising showings with Arrows but then they went out of business, owing Frentzen more money. Back with Sauber for 2003, Frentzen managed a mini-renaissance, proving himself more than a match for his highly-rated team mate Nick Heidfeld and even scoring a podium finish in the penultimate race of the year in the United States.
For 2004, Frentzen moved to the German Deutsche Tourenwagen Masters saloon car series to drive for Opel, encouraged by the success achieved in the series by fellow F1 refugee Jean Alesi. Unfortunately his Opel Vectra was not a competitive car, and he was regularly outpaced by not only the Audi and Mercedes drivers but also by his Opel teammates, eventually finishing the season 14th in the championship standings. However he remained in the DTM with Opel for the 2005 season and finished the year in 8th as best-placed Opel driver, with his best result a 3rd place from pole position at Brno in the Czech Republic.
Opel withdrew after the 2005 season, with Frentzen moving to Audi for 2006. By the first race 2006 in Hockenheim he finished at 3rd.