The 34-year-old, competing in the mythic race for the seventh time, spun off on the third lap into the safety barriers
Simonsen was transferred to the circuit's medical centre where he succumbed to his injuries shortly after, organisers announced.
Simonsen crashed barely ten minutes after the start of the 81st edition of the showpiece endurance event with rain and wind combining to make testing conditions at the Sarthe circuit.
Officials stopped the race for an hour, the time required to repair the safety barrier.
Simonsen, driving an Aston Martin V8 Vantage, was competing in the GTE-Am category.