Casimir de Marcassus was born in Toulouse to a distinguished family.
His grandfather and father both served as governing magistrates for the Capitole de Toulouse.
He married Marie-Antoinette Good, and lived and worked in Toulouse his entire life.
Casimir de Marcassus was a chemist who introduced into France glass etching by hydrofluoric acid.
Following in his father's footsteps he became councilor of Toulouse and general counsel of the Haute-Garonne.