Pre-WWII de Gaulle was already a kind of celebrity in military circles. Wags would out it that he certainly was cut out for the "Academie", by which they did not mean the "École militaire" but the "Academie française", since he wrote a lot, in a punchy style . (Just one of the aspects in which de Gaille and Churchill resembled each other.)
He had been hired already as Pétain's ghost-writer – except the arrangement fell apart when it became apparent that de Gaulle still insisted on writing what HE thought, not necessarily what Pétain wanted.
And Pétain had interceded to bump up his grades from the military academy to give him the kind of possible career trajectory Pétain thought he should have.
And he had cause a scandal when invited to give a series of lectures on the future of combat (armoured and mobile) at the École militaire, which had ended with his posting in the colonies overseas to get everyone out of embarassment. (Never actually went there though iirc.)
So de Gaulle was clearly a man to watch, not just militarily, already before WWII. Then it didn't hurt him that he actually got to put some of his ideas about armoured warfare to the test in 1940, and did well enough to earn a temporary brigadeer's grade, and a spot as a junior minster in the last Reynaud government before the roof caved in, and de Gaulle hopped on a plane to London to keep fighting.