Before the race, Toyota drivers Fernando Alonso, Sebastien Buemi and Kazuki Nakajima led the LMP Drivers' Championship with 26 points, eight ahead of teammates Mike Conway, Kamui Kobayashi and Jose Maria Lopez. In the GTE Drivers' Championship, Billy Johnson, Stefan Mucke and Olivier Pla of Ford Chip Ganassi Racing led with 25 points. Toyota held a commanding lead in the LMP1 Teams' Championship, while Porsche led Ford in the GTE Manufacturers' Championship.
Following the 2017 race, modifications were made to the Porsche Curves section of the Circuit de la Sarthe to improve safety. Barriers on the inside of the final right-hand corner were relocated further from the track, allowing for the construction of paved run-off areas and escape roads. These changes re-profiled the corner slightly, shortening the overall lap distance by three metres. The ACO also installed a new starting gantry 145 metres further up the main straight to increase capacity at the start, while the finish line and all timing beacons remained at the original position at the exit of the Ford Chicane.
The No. 8 Toyota TS050 Hybrid of Buemi, Nakajima and Alonso started from pole position after Nakajima recorded the fastest qualifying lap. The two Toyota entries exchanged the lead through the first half of the race until Buemi received a one-minute stop-and-go penalty for speeding in a safety-enforced slow zone after a night-time accident. This dropped the No. 8 car behind its sister entry. Alonso and Nakajima retook the lead from Conway, Kobayashi and Lopez in the 16th hour and maintained it to the finish. It was the first Le Mans victory for Alonso, Buemi and Nakajima, and Toyota's first overall win in 20 attempts at the circuit. The sister No. 7 Toyota of Conway, Kobayashi and Lopez finished two laps behind in second. A Rebellion R13 driven by Thomas Laurent, Gustavo Menezes and Mathias Beche completed the overall podium in third.
The G-Drive Racing Oreca 07 of Roman Rusinov, Andrea Pizzitola and Jean-Eric Vergne led 360 consecutive laps and was the first car to complete the race. The team was subsequently disqualified for running an illegal refuelling component, and a G-Drive appeal was rejected. Class victory was awarded to the Signatech Alpine team of Nicolas Lapierre, Pierre Thiriet and Andre Negrao. A Graff-SO24 car shared by Vincent Capillaire, Jonathan Hirschi and Tristan Gommendy finished second, with a United Autosports Ligier JS P217 driven by Hugo de Sadeleer, Will Owen and Juan Pablo Montoya third.
On its 70th anniversary, Porsche won both GT categories. In LMGTE Pro, the No. 92 Porsche 911 RSR of Michael Christensen, Kevin Estre and Laurens Vanthoor finished ahead of the No. 91 car of Richard Lietz, Gianmaria Bruni and Frederic Makowiecki. In LMGTE Am, Dempsey-Proton Racing's trio of Matt Campbell, Christian Ried and Julien Andlauer took the class win.
The result moved Alonso, Buemi and Nakajima 20 points clear of Conway, Kobayashi and Lopez in the LMP Drivers' Championship. In the GTE Drivers' Championship, Christensen and Estre took the lead from Johnson, Mucke and Pla. Toyota further extended their advantage over Rebellion Racing in the LMP1 Teams' Championship to 27 points, while Porsche extended its lead over Ford in the GTE Manufacturers' Championship with six rounds remaining.
The 2018 race ended Toyota's long wait for a Le Mans victory and brought Fernando Alonso the final leg of a rare endurance racing triple crown, having already won the Indianapolis 500 in 2017 and the Formula One World Championship twice previously. The G-Drive disqualification also highlighted the stringent technical regulations governing refuelling systems, with teams facing elimination even after dominating their class for most of the race.