The 1970 race marked the last year in which five-litre Group 5 sports cars were eligible, having been given notice that the limit would fall to three litres for 1972. The CSI's revised Appendix J redefined class structures: Group 4 covered Special GT cars requiring 500 units of production, Group 5 covered Sports Cars (minimum 25 cars built), and Group 6 remained for Prototypes. The Automobile Club de l'Ouest introduced three-driver crews, permitted a single mid-race car transfer between cars of the same make, and set a 14-hour maximum driving time per driver. The most celebrated change was the abolition of the traditional Le Mans start: instead of drivers sprinting across the track to their cars, they were now required to be fully strapped in before the flag dropped.
Safety upgrades included a further 12 km of Armco barrier completing the circuit's perimeter, and widening of the Esses and Tertre Rouge corners. The entry ran to 57 starters from 62 accepted — the absence of Ford and Alpine was notable — with almost a third of the grid made up of the two headline competitors, Porsche and Ferrari.
Porsche arrived having fixed the 917's stability problems from 1969. Working with John Wyer and his Gulf-J.W. Automotive Engineering team as the official works partner, engineer John Horsmann developed the short-tail 917K (kurzheck), which offered better stability than the spectacular long-tail 917L (langheck). Nine 917s were entered in total across JWAE, Porsche Salzburg (run by Louise Piëch, sister of Ferry Porsche), and the Martini Racing team. Ferrari countered with eleven 512S entries — a freshly homologated Group 5 car based on the 612 Can-Am machine, fitted with a 5.0-litre V12 producing around 550 bhp. Eight 512s ran in long-tail (coda lunga) configuration.
The long-tail Porsches dominated qualifying. Vic Elford set the fastest lap of 3:19.8 in the Porsche Salzburg 917L to claim pole position, fractionally quicker than Nino Vaccarella's Ferrari. The Wyer Porsches of Jo Siffert and Pedro Rodriguez qualified third and fifth. Hermann and Attwood's third Salzburg 917K started from 15th after brake difficulties.
The race started at 4pm, with guest starter Dr Ferry Porsche marking the marque's 20th Le Mans. The opening laps saw Elford, Siffert, and Rodriguez quickly establish themselves at the front. Rain arrived at 5:30pm and lasted through the night, transforming the race. Vaccarella's Ferrari retired after just seven laps with a broken crankshaft. Pedro Rodriguez's JWAE Porsche stopped at Arnage with cooling fan failure after only 23 laps. In a single rain-induced accident at Maison Blanche, four Ferrari 512s were eliminated simultaneously when Clay Regazzoni and Mike Parkes struck Reine Wisell's stalled car and were themselves hit by Sam Posey; Derek Bell's engine failed on the same lap from excessive downshifting. Parkes suffered minor burns.
Siffert and Elford traded the lead through the night. All three Matras retired with leaking piston rings within ten laps of each other, ending the French prototype challenge within four hours. Jacky Ickx staged an impressive charge through the rain in the works Ferrari, climbing to second place by midnight. At 1:45am Ickx's run ended when rear brake failure sent him into a sandbank at the Ford Chicane; the car burst into flame, killing track marshal Jacques Argoud. Siffert's commanding lead evaporated when he missed a gear change while lapping backmarkers, breaking the engine. At half-distance the lead had passed to the Herrmann/Attwood Salzburg 917K, which had been running consistently from its 15th grid position.
Dawn brought a storm. By 6am Porsche held the top four positions: Herrmann/Attwood leading, Elford/Ahrens second, the Martini 908 of Lins/Marko third, and Larrousse/Kauhsen's Martini longtail fourth. Elford retired with engine problems at 8:30am. By midday, and with the track drying, Larrousse/Kauhsen moved up to second but could not close the five-lap deficit to the leaders. Only seven cars were classified as finishers. Herrmann and Attwood took the victory in a race veteran's most poignant triumph: Herrmann, competing at Le Mans for the 14th time, had lost the 1969 race by the narrowest of margins. Porsche swept all three class awards and every class win. The overall result cemented Porsche's dominance in the 1970 Championship for Makes.
The 1970 race provided the backdrop for the Steve McQueen film Le Mans. Solar Productions — McQueen's company — entered a Porsche 908-022 fitted with cameras, crewed by Herbert Linge and Jonathan Williams. A proposed entry for McQueen himself and reigning F1 champion Jackie Stewart was not accepted by the ACO. Some race footage from the camera car appeared in the final film, though much of the on-board material proved technically unusable.