Fermat is easily one of the best known mathematicians of all time. We all know about Fermat's Last Theorem, Fermat's Little Theorem, his quadrature rule, his invention of probability theory, etc. Every introduction of Fermat, however, mentions that mathematics wasn't his "day job" and that he was a lawyer.

As much as I search, I cannot seem to find anything on his work as a lawyer. Unless his job was divine mathematics as a lawyer, I get the feeling that his work as a lawyer was either unremarkable or just forgotten.

Does anyone have a reference that they can point me to that could describe his role in law? Or something that would tell me what his job would have been?