Fath grew up in postwar Germany and came to motorcycle racing as both a competitor and a builder. His early outfits were based on BMW R50 sidecars fitted to chassis of his own construction, a hands-on approach that distinguished him from rivals who relied on factory equipment. This engineering instinct would prove to be the defining thread of his career.
Fath won his first Sidecar World Championship in 1960, competing in the 500cc sidecar class that was then the premier category of the discipline. The title demonstrated that a privateer operating without full factory backing could compete at the highest level of the world championship, provided the combination of driver and machinery was strong enough.
In 1961, Fath suffered a serious accident that forced him to step back from racing. Rather than retire, he used the recovery period to pursue an ambition that had long occupied him: designing and building his own racing engine from scratch. Over several years he developed a four-cylinder unit designated the URS, named after Ursenbach, the area associated with his workshop.
When Fath returned to competition, he did so with the URS-powered outfit. In 1968 he won the Sidecar World Championship for a second time, making him one of only a handful of competitors in the history of grand prix motorcycle racing to have won a world title aboard machinery powered by an engine entirely of their own design. The achievement underlined how far outside the mainstream of factory-supported racing a determined engineer-racer could operate and still reach the top.
The URS four-cylinder engine proved its quality beyond Fath's own riding career. It went on to power Horst Owesle and passenger Peter Rutterford to the 1971 Sidecar World Championship, confirming that the design was not merely competitive when piloted by its creator but represented a genuinely superior piece of engineering for the era. The engine's longevity in competition — achieving championship success across two different pairings — gave Fath a lasting legacy as a constructor as well as a racer.
Fath's career spans the transition from the early years of the FIM World Championship to the late 1960s, a period in which the sidecar class attracted serious engineering effort. His two world titles, separated by a near-fatal accident and years of mechanical development, trace an unusually dramatic arc. That both titles came without the backing of a major manufacturer placed Fath among the most self-reliant champions the sport produced. He died on 19 June 1993.