The circuit's creation is credited to Jules de Thier, owner of the Liège newspaper La Meuse, who identified the public roads connecting Spa-Francorchamps, Malmedy, and Stavelot as an ideal racing venue. Following a meeting at the Hôtel des Bruyères in Francorchamps with burgomaster Joseph de Crawhez and racing driver Henri Langlois van Ophem, the triangular route was adopted. The Eau Rouge creek, which marked the former Belgian-German Empire border until 1920, lay at the foot of the circuit's most famous section.
The track's inaugural race was planned for August 1921 but cancelled when only one driver entered. The first competitive motor race was held in 1922, and in 1924 the circuit saw the inaugural 24 Hours of Francorchamps endurance race. The circuit was first used for Grand Prix racing in 1925.
In its final pre-1979 form, the original circuit measured 14.100 km (8.761 mi), making it one of the longest road courses in regular use. It was essentially a sustained high-speed course; drivers averaged over 240 km/h (150 mph) in competitive conditions during its final years, and the fastest cars barely reduced speed through any corner. The 1973 lap record of 3 minutes 13.4 seconds, set by Henri Pescarolo in a Matra during the 1000 km Spa world sportscar race, represented an average speed of 262 km/h (163 mph). The fastest-ever recorded time on the old circuit was the pole position for that same race: 3 minutes 12.7 seconds, set by Jacky Ickx in a Ferrari 312PB.
Key landmarks included the Eau Rouge stream crossing, after which cars were launched steeply uphill via the Raidillon corner added in 1939; the Masta Kink, a flat-out high-speed left-right chicane between two long straights running past farmhouses near Malmedy; and the town of Stavelot, where a sharp original hairpin was eventually replaced by a quicker banked sweep. The public roads used by the circuit remained open to civilian traffic for much of the year, with houses, trees, and electric poles lining the racing surface.
The circuit underwent several changes between its opening and its closure. In 1930 the Malmedy chicane was eliminated to raise speeds, but was reinstated in 1935. In 1939 the slow uphill Ancienne Douane hairpin at the foot of Eau Rouge was cut short to create the sweeping Raidillon, decisively increasing lap speeds through this sector. In 1947 the Malmedy chicane was again removed, and the Hollowell section was altered so that rather than passing through the streets of Stavelot the track took a fast wide right-hander bypassing the town entirely. These successive changes made the final version of the circuit faster at every revision.
The circuit's safety record was grave. Ten drivers died in car racing accidents at Spa in the 1960s alone, five of them in the final two years of that decade. The 1960 Belgian Grand Prix saw two drivers, Chris Bristow and Alan Stacey, killed within fifteen minutes of each other during the race. Stirling Moss was severely injured in practice that same year. The extreme danger prompted a boycott of the 1969 Belgian Grand Prix by Formula One drivers.
Jackie Stewart, who crashed his BRM at the Masta Kink during the 1966 Belgian Grand Prix and was trapped in the car with fuel flooding over him, later described the old Spa circuit as "as ferocious as a tiger" and called Masta perhaps the hardest corner on any track he raced in his career. Armco barriers were added for the 1970 race, but multiple fatalities during the 1973 and 1975 editions of the 24 Hours of Spa touring car race accelerated calls for change.
The last Formula One race on the original layout was the 1970 Belgian Grand Prix. Formula One did not return to Spa until 1983, by which point a redesigned permanent circuit of 6.947 km (4.317 mi) had been constructed. The old 14.100 km layout hosted its final major events during the late 1970s; by 1978 only the Belgian motorcycle Grand Prix and the 24 Hours of Spa touring car race remained on the calendar. The 1979 redesign brought an end to the original circuit's competitive life.
Eighteen Formula One World Championship Grands Prix were held on the original Spa-Francorchamps layout between 1925 and 1970. The circuit is remembered as the supreme test of driver ability during its era: a lap lasting approximately three to four minutes at near-maximum speed throughout, with almost no corners below 290 km/h (180 mph) for the fastest cars. Its combination of extreme speed, unpredictable Ardennes weather that could produce dry conditions at one sector and heavy rain at another, and minimal safety infrastructure made it both the most demanding and the most dangerous road circuit of its time.