The 21-year-old was well ahead of teammate Sebastian Vettel, who only managed to put his SF90 on P7 in a disappointing outing for the four-time champion.
Leclerc, who is usually quite hard on himself, was actually quite pleased with his own performance at the very windy Paul Ricard.
"At the end, pretty happy with my lap," Leclerc said in his on-grid interview after qualifying.
"Unfortunately, today it wasn't enough. We need to keep working and I'm pretty sure we'll close the gap [to Mercedes] at one point.
"But today, it's the best result we could've got. Hopefully, tomorrow will be a good race."