Following the end of World War I, Jules de Thier, owner of the Liège newspaper La Meuse, sought a site to host a race. After a meeting at the Hotel des Bruyères in Francorchamps with burgomaster Joseph de Crawhez and racing driver Henri Langlois van Ophem, the roads connecting Spa-Francorchamps to the former German town of Malmedy, south to Stavelot, and back towards Francorchamps were identified as an ideal triangle-shaped circuit with few tight corners and long fast sections. The track's inaugural race was planned for August 1921 but cancelled when only one driver entered. The first car race was held in 1922, and the first 24 Hours of Francorchamps took place in 1924. The circuit was first used for Grand Prix racing in 1925.
The old circuit traced a route through the Ardennes countryside entirely on public roads, with houses, trees, telegraph poles, and fields immediately adjacent to the track surface. Before 1970, safety provisions amounted to little more than straw bales.
From the start-finish straight before La Source hairpin, drivers descended towards the Eau Rouge creek crossing and then climbed steeply through the Raidillon — a sweeping uphill corner cut in 1939 to replace a slower U-turn. The track then continued through the Kemmel curves (straightened in 1979) to the highest point of the circuit, 102.2 m above the lowest point, before dropping into Les Combes and sweeping through Burnenville. The Masta Straight then began, interrupted only by the Masta Kink — a high-speed left-right chicane set between farmhouses — before arriving at Stavelot. After Stavelot, the track climbed through La Carriere, passed Blanchimont, and braked hard for La Source hairpin to rejoin the start-finish section.
The final configuration before the 1979 redesign measured 14.100 km (8.761 mi). In the last years of the old layout, drivers averaged 240 km/h (150 mph) over an entire lap. Most corners were taken at more than 290 km/h (180 mph), offering no margin for error: a slight lift cost whole seconds, not tenths.
Jackie Stewart, who drove there in the 1960s, described the Masta Kink as "by far the most difficult corner in the world." Set between two straights each approximately 2.4 km (1.5 mi) long, the kink could be approached at up to 298 km/h (185 mph). Stewart's concern with safety at Spa was galvanised by his own crash at Masta in 1966, when his BRM ended upside-down in a ditch with fuel pouring over him. He later described the old Spa circuit as being "as ferocious as a tiger" and ranked Masta as perhaps the hardest corner he raced on in his career, exceeding even Eau Rouge in its demands.
Before 1970, the circuit had no Armco barriers of any kind. Fatalities were a recurrent feature: at the 1960 Belgian Grand Prix, two drivers — Chris Bristow and Alan Stacey — were killed within fifteen minutes of each other, and Stirling Moss was severely injured in practice at Burnenville. In 1969, Formula One drivers boycotted the Belgian Grand Prix entirely due to safety concerns, citing ten fatalities at the circuit during the 1960s, five in the preceding two years alone. The race was dropped from the calendar that year; Armco barriers were subsequently installed, and sections of the circuit at Stavelot and Hollowell were improved. Even so, the 1970 race — run with a temporary chicane inserted at Malmedy — averaged over 240 km/h (150 mph) for the entire field, which drivers still considered unacceptable. Formula One did not return to Spa until 1983, on the modern track.
Multiple fatalities during the 1973 and 1975 24 Hours of Spa touring car races effectively sealed the old circuit's fate. By 1978, the last year the original layout was used for any racing, only the Belgian motorcycle Grand Prix and the Spa 24 Hours touring car race remained on it; the World Sportscar Championship 1000 km race had ended after 1975.
The lap record of the old triangle circuit — 3 minutes 13.4 seconds — was set by Henri Pescarolo in a Matra at the 1973 Spa 1000 km World Sportscar Championship race, at an average speed of 262 km/h (163 mph). The fastest recorded time on the old layout was the pole position for that same race: 3 minutes 12.7 seconds, set by Jacky Ickx in a Ferrari 312PB.
The circuit was shortened from 14.100 km to 6.947 km in 1979, with the new permanent track retaining some of the old road sections and the famous Raidillon de l'Eau Rouge. The start-finish line was moved to the straight before La Source hairpin in 1981. The new layout, while still regarded as one of the most challenging circuits in motorsport, eliminated the sustained high-speed public-road sections that had defined the original Spa-Francorchamps.