(Does anyone else think it's unfair that Chauvelin was a real person but Sir Percy is fiction???)
Citizen Chauvelin is loosely based on Bernard-François, marquis de Chauvelin, a real official during the French revolution. According to my highly reliable source (which is really the much fail-able Wikipedia), the real Chauvelin is not much like the books' portrayal at all.
Here are some basic fact about the man:
1) he was actually of noble birth (His father was Master of the King's Wardrobe! How's that for a job title...) but had liberal tendencies and welcomed the Revolution.
2) He really was an ambassador for the "new" France.
3) he was an outstanding orator
4) He died in April of 1832 of cholera
I did find information once that said he was married, but I can't remember the reference and so cannot vouch for it. I have not been able to find anything about a marriage since. He is not especially well-kown; I could not find much more information or any picture of what he really looked like.