As the director-general of the CNRS, albeit briefly, from 13 to 18 June 1940,[4] he destroyed scientific equipment in his laboratories to prevent it from falling into German hands.

He later established a charcoal production facility in the forests of Auvergne that also served as a haven for those evading the compulsory labor service (STO).

On 6 February 1947, he was elected to the Council of the Republic of France to represent French citizens abroad, aligning with the Democratic Left group.

In the early 1950s, Longchambon initiated the creation of a major national institute dedicated to engineering education and applied research.

With support from Lyon’s regional authorities, the government, and Parliament, the Institut national des sciences appliquées (INSA) was established in 1957 in Villeurbanne, Rhône.

Investigative work by journalist Hervé Laronde revealed that the car, one of twenty prototypes, was stolen from Longchambon's widow in 1980.