In the early 1920s, the circuit ran from the present pits on Rue de Laigné straight into the city of Le Mans, took a sharp right-hand corner near the Huisne River at the Pontlieue bridge — a hairpin that would remain a feature until 1929 — and then left the city along the section later named Avenue Georges Durand, after the race's founder. The course then ran south to the village of Mulsanne, turned northwest to Arnage, and returned north to Le Mans.
In this earliest form the circuit measured approximately 17.261 km (10.725 mi) and was entirely unpaved. Its character was that of a fast open-road course through the French countryside, with few significant corners beyond the Pontlieue hairpin and the Mulsanne and Arnage turns.
The circuit hosted its inaugural events in 1923, with the first running of the 24 Hours of Le Mans taking place on 26 to 27 May 1923. That first edition established the endurance format that would define the event: teams of two drivers sharing a car for twenty-four consecutive hours, racing on the same public roads used by everyday traffic for the rest of the year. The winner of the first 24 Hours of Le Mans was the French crew of André Lagache and René Léonard in a Chenard et Walcker, covering 2,209.536 km at an average speed of 92.064 km/h (57.2 mph).
In 1929 a bypass within the city of Le Mans was built, shortening the circuit by removing the Pontlieue hairpin section through the city centre. This reduced the overall lap length and moved the course's urban section away from the streets closest to the river. In 1932 the city was bypassed completely with the addition of a section from the pits via a new bridge over the railway — later known as the Dunlop Bridge — and through a series of corners leading to Tertre Rouge and onto the Mulsanne Straight. This 1932 revision produced what is often called the "classic circuit" configuration of 13.492 km (8.384 mi), which remained largely unaltered until 1972.
In its original 1920s form the circuit's dominant feature was the long straight running south through the Sarthe countryside toward Mulsanne, which would later become world-famous as the Hunaudières straight. Cars spent extended periods at full throttle in this sector. The pit straight itself was extremely narrow — approximately 3.7 m (12 ft) wide — as it was simply a section of the public road without any widening to accommodate the pits, and the racing surface was not separated from the pit area by any barrier.
The track surface was unpaved in the earliest years. Roads were open to public traffic outside race periods, and the circuit's infrastructure was minimal by later standards. This early configuration set the endurance and mechanical reliability demands that would characterise Le Mans throughout its history: sustained high-speed running on public roads with limited intervention.
The Circuit de la Sarthe's original 1920s layout was the birthplace of the 24 Hours of Le Mans, an event that grew into the most prestigious sports car race in the world. The geographic triangle between Le Mans, Mulsanne, and Arnage that defined the earliest layout remains — in modified form — the structural backbone of every subsequent configuration. The Mulsanne Straight, which derived from the long open road southward toward the village of the same name, survived in its original form until 1990 when two chicanes were added to limit maximum speeds that had exceeded 400 km/h (250 mph) in the late 1980s.