I've seen him credited as co-designer of the proposed Wimille electric car project during the occupation of France, which evolved into the conventionally powered road car that went through several prototype iterations from 1946 onwards. He was apparently Wimille's personal manager and also the Bugatti team's pit manager at some point. I also have a note that he sheltered Wimille's wife Christiane after she narrowly escaped deportation to Germany in 1944.
If anyone has a copy of Les Véhicules de l'Occupation by Jacques Borgé & Nicolas Viasnoff (Balland 1975) he gets at least a couple of mentions, according to some snippet views on Gallica.
A Pierre Leygonie of 43 boulevard Inkermann, Neuilly-sur-Seine, offered an 'impeccable' Voisin 14HP for sale in L'Auto, 1 July 1931, p4 - he's presumably our man?
This is probably a red herring, but it's possible that he was originally from Algeria - a search of Gallica brings up a Pierre Leygonie (and a M & Mme Jean Leygonie) among a long list of people offering condolences on a death in 1927 - La Dépêche algérienne 17 March 1927, p3 - and in another publication (L'Hippique algérienne et tunisienne) there are references to a 'gentleman Pierre Leygonie'; a 1918 issue of La Dépêche algérienne has a small ad from a Pierre Leygonie of Villa Bagatelle, Kouba, who is selling a horse and appears to be the same man. Kouba is a suburb of Algiers. However, he also seems to have later been a dog breeder, so possibly not the same Pierre Leygonie.
ETA: looks like it was a red herring!