The circuit was conceived by Jules de Thier, owner of the Liège newspaper La Meuse. Following a meeting at the Hotel des Bruyères in Francorchamps with burgomaster Joseph de Crawhez and racing driver Henri Langlois van Ophem, it was agreed that the triangle of public roads linking Francorchamps to Malmedy, south to Stavelot, and back again constituted an ideal racing course. The roads offered few tight corners and long, fast sections through Ardennes forest.
The track's inaugural race was planned for August 1921 but was cancelled when only one driver entered. The first car race was held in 1922, and 1924 saw the debut of the 24 Hours of Francorchamps endurance race. Grand Prix racing arrived in 1925. The course ran clockwise: from the start-finish straight on the downhill before Eau Rouge, down through the Eau Rouge creek valley, up the Kemmel curves, over the highest point of the circuit, down through Les Combes and Burnenville, along the Masta straight past the notorious Masta Kink, through the town of Stavelot, then back via La Carriere, Blanchimont, and the La Source hairpin.
The original Spa-Stavelot circuit was distinguished above all by sustained high speed. Drivers experienced virtually no reduction in velocity throughout a lap that lasted around three to four minutes. By its final years, drivers were averaging 240 km/h (150 mph), and in its fastest recorded time — the 1973 Spa 1000 km pole position set by Jacky Ickx in a Ferrari 312PB — a lap was completed in 3 minutes 12.7 seconds. The lap record set during a race was 3 minutes 13.4 seconds, recorded by Henri Pescarolo driving a Matra at the 1973 Spa 1000 km at an average of 262 km/h (163 mph).
The circuit underwent several configuration changes over the decades. In 1930 the Malmedy chicane was removed to make the course faster, though it was reinstated in 1935. In 1939 the Ancienne Douane hairpin at Eau Rouge was cut short and replaced with the sweeping uphill Raidillon. The Malmedy chicane was again bypassed in 1947, and the Stavelot hairpin was replaced by a fast banked right-hand bypass. These revisions brought the circuit to its final length of 14.100 km and made it the fastest open road circuit in the world.
Among the circuit's defining features was the Masta Kink, which Jackie Stewart described as "by far the most difficult corner in the world." Situated mid-way along the Masta straight — between two unbroken straight sections each approximately 2.4 km long — the Masta Kink was a high-speed left-right chicane where cars could reach 298 km/h (185 mph). The corner demanded a clean entry and exit, because a poor line cost many seconds on the subsequent long run to Stavelot.
Stewart's own opinion of the Kink was shaped by personal experience: in 1966 his BRM ended upside-down in a ditch near a farmhouse at Masta, fuel pouring over him as he sat with broken ribs, unable to escape the cockpit. He would later describe the old Spa circuit in 1986 as "ferocious as a tiger" and, in 2011, called Masta the hardest corner he ever raced on — harder even than Eau Rouge.
Because the course ran on ordinary public roads, there were houses, trees, electric poles, and fields immediately beside the racing surface. Before 1970, virtually no safety modifications existed beyond a few straw bales. Racing drivers widely regarded the circuit as among the most dangerous in the world, and several boycotted or refused to race there.
At the 1960 Belgian Grand Prix, two drivers, Chris Bristow and Alan Stacey, were killed within fifteen minutes of each other; Stirling Moss was severely injured in practice at Burnenville during the same weekend. The 1969 Belgian Grand Prix was cancelled after drivers boycotted on safety grounds — the circuit had recorded ten car racing fatalities during the 1960s alone, five of them in the preceding two years. Armco barriers were installed in 1970 and further track improvements made, including a temporary chicane at Malmedy, but drivers still averaged over 240 km/h even with the chicane in place.
Multiple fatalities during the 1973 and 1975 24 Hours of Spa touring car races effectively sealed the old circuit's fate. By 1978, the only major events held on the original layout were the Belgian motorcycle Grand Prix and the Spa 24 Hours. Eighteen Formula One World Championship Grands Prix had been run on the original configuration before Formula One left for good after the 1970 race.
In 1979 the circuit was shortened from 14.100 km to 6.947 km, abandoning the Malmedy and Masta sections entirely and replacing them with a new permanent infield section that rejoined the old layout at Blanchimont. The new start-finish straight was moved in 1981 to the section before La Source.
The Eau Rouge–Raidillon combination and the La Source hairpin survive as key elements of the modern Spa-Francorchamps circuit. The old road sections to Malmedy and Stavelot reverted to public use, with some stretches becoming cul-de-sacs. The original layout remains celebrated for producing some of the highest sustained speeds in the history of Grand Prix racing, and the circuit's reputation for unpredictable Ardennes weather — which could produce rain on one section while sunshine fell on another — added a further dimension of danger that drivers of the era never forgot.