Herrmann was a baker by trade before becoming a professional racing driver. His career began in an era that still featured legendary road races such as the Mille Miglia, Targa Florio, and Carrera Panamericana, and he is one of the last witnesses of that period. His longevity was remarkable: he died on 9 January 2026 at the age of 97, having outlived the next-oldest survivor from that era by several years.
The most celebrated of his escapes came at the 1954 Mille Miglia. Driving a very low Porsche 550 Spyder with navigator Herbert Linge, Herrmann arrived at a railway crossing to find the gates closing for the fast Rome express. Judging it too late to brake, he knocked on Linge's helmet to make him duck, and they passed beneath the descending barriers with the train passing immediately behind them.
From 1954 to 1955 Herrmann was a junior works driver for Mercedes-Benz in Formula One, operating behind Juan Manuel Fangio, Karl Kling, Hermann Lang, and later Stirling Moss. At the 1954 French Grand Prix, where the Silver Arrows returned after a long absence to score a 1–2 finish, Herrmann set the fastest lap but retired. His best championship result with the team was a podium at the 1954 Swiss Grand Prix, often achieved in older or less reliable versions of the Mercedes-Benz W196.
In 1955 he shared a car with Kling and Moss at the Argentine Grand Prix under the extreme heat conditions, gaining one shared point each. A crash in practice at Monaco that year ended his participation in what would prove to be an ill-fated season, in which the Le Mans disaster led Mercedes-Benz to withdraw from racing entirely.
After Mercedes-Benz's withdrawal Herrmann raced in Formula One for Cooper, Maserati, and BRM. At the 1959 German Grand Prix at Berlin's AVUS, brake failure sent his BRM into a spectacular crash, the car somersaulting as Herrmann was thrown clear and slid along the track.
With Porsche's 718 sportscars and Formula Two cars he scored victories at the 1960 12 Hours of Sebring and the Targa Florio. When the Porsche 718 became eligible for Formula One in 1961 under the new 1.5-litre rules, results were disappointing. Herrmann left Porsche in early 1962, feeling overlooked in favour of Dan Gurney and Jo Bonnier.
From 1962 to 1965 he raced small Abarth cars in minor events and hillclimbs, gaining experience in testing and development that would serve him well. He returned to Porsche in 1966 for a comeback in the World Sportscar Championship.
Back at Porsche, Herrmann accumulated podiums with the Porsche 906 and subsequent models. In 1968 he won the 24 Hours of Daytona in a Porsche 907 and the 12 Hours of Sebring again, now co-driving with Swiss driver Jo Siffert. He narrowly missed the 1969 Le Mans overall win with a Porsche 908, losing by only 120 metres.
The following year Herrmann finally achieved what had eluded him: the first overall Porsche victory at the 24 Hours of Le Mans. Driving for the Porsche Salzburg factory-backed team in the distinctive Austrian red and white livery, he and co-driver Richard Attwood survived heavy rain and attrition in a Porsche 917K to win as the best of only seven finishers.
Before the race, Herrmann had half-jokingly promised his wife he would retire if he won at Le Mans. He was 42. Having witnessed the fatal accidents of too many colleagues — including his neighbour and teammate Gerhard Mitter, who died before the 1969 German Grand Prix — he kept his word and announced his retirement on television after driving the winning car in a parade from the Porsche factory through Stuttgart to the town hall.
Herrmann subsequently built a successful automotive supplies business using his industry contacts. He remained engaged in the racing community into his nineties, demonstrating historic cars at events including the Solitude Revival. He was kidnapped once in the 1990s and held in a car boot for many hours before escaping. After the death of Tony Brooks in 2022, Herrmann became the last surviving Formula One podium finisher from the 1950s, a status he held until his death in January 2026.