Herrmann's introduction to high-stakes motorsport came through the legendary long-distance road races of the early 1950s. He participated in the Mille Miglia, the Targa Florio, and the Carrera Panamericana, becoming one of a small group of drivers who could claim intimate knowledge of that era. His most celebrated early moment came at the 1954 Mille Miglia, when a railroad crossing barrier descended in front of his Porsche 550 Spyder at full speed. With no time to brake, Herrmann signaled his co-driver Herbert Linge to duck, and the low-slung car passed beneath the barrier and clear of the oncoming train, stunning onlookers.
From 1954 to 1955, Herrmann joined the Mercedes-Benz factory team as a junior driver behind Juan Manuel Fangio, Karl Kling, Hermann Lang, and later Stirling Moss. When the Silver Arrows returned for the 1954 French Grand Prix, Herrmann set the fastest lap but was forced to retire. His best championship result came at the 1954 Swiss Grand Prix, where he reached the podium despite being assigned the older and less reliable versions of the Mercedes-Benz W196.
The 1955 season proved difficult. In the Argentine Grand Prix, Herrmann shared his car with teammates Kling and Moss after they retired from the intense heat, earning a fourth-place finish. He was competitive in the Mille Miglia with the Mercedes-Benz 300 SLR but had to abandon. A crash in practice for the Monaco Grand Prix ended his season early, cutting short a planned return at the Targa Florio.
After Mercedes withdrew from racing, Herrmann drove for Cooper, Maserati, and BRM in Formula One. He finished 19 World Championship Grands Prix in total and scored 10 championship points. A dramatic incident came at the 1959 German Grand Prix at the AVUS circuit, when his BRM's brakes failed and he crashed spectacularly, being thrown from the car as it somersaulted through the air. He survived without serious injury.
With the Porsche 718 in its various configurations — sportscar, Formula Two, and eventually Formula One specification — Herrmann scored wins in the 1960 12 Hours of Sebring and the Targa Florio. When the Porsche 718 single-seater became eligible for Formula One in 1961 following rule changes, results were modest; he finished last in the 1961 Dutch Grand Prix, which was also the first Formula One World Championship race completed without a single retirement. He departed Porsche in early 1962, feeling overshadowed by the team's preference for Dan Gurney and Jo Bonnier.
Between 1962 and 1965, Herrmann drove for Italian constructor Abarth in minor sports car races and hillclimbing events. Though the small Abarths were competitive in their displacement classes from 850cc to 1600cc, outright victories came only at lesser events such as the AVUS or the 500 km Nürburgring. The experience taught Herrmann a great deal about car development and testing, skills that would prove valuable in his later Porsche years.
In 1966, Herrmann rejoined Porsche for the World Sportscar Championship as the manufacturer launched a serious assault on endurance racing. He quickly returned to winning form, claiming the 1968 24 Hours of Daytona in a Porsche 907 alongside Jo Siffert, and the 1968 12 Hours of Sebring, also with Siffert. He finished second in the 1000 km Nürburgring three consecutive times between 1968 and 1970, each time behind his own teammates.
The 1969 24 Hours of Le Mans brought one of the closest finishes in the race's history, with Herrmann and his Porsche 908 losing by just 120 metres to Jacky Ickx. A year later, at the 1970 24 Hours of Le Mans, Herrmann finally secured the victory that Porsche had long sought. Driving the Porsche 917K No. 23 for Porsche Salzburg — the Austrian factory-backed team owned by the Porsche family — alongside Richard Attwood, he navigated torrential rain to finish best among only seven classified finishers.
Herrmann had made a half-serious promise to his wife that he would retire if he won Le Mans. Haunted by the deaths of colleagues over many years, including that of his neighbour Gerhard Mitter before the 1969 German Grand Prix, the 42-year-old announced his retirement on television after a parade through Stuttgart in the winning car. He then built a successful automotive supply company. Herrmann remained active in the historic racing community into old age, demonstrating cars at events such as the Solitude Revival. He died on 9 January 2026, aged 97.