A method for manufacturing a continuous carbon fiber from a precursor material. According to this method, a precursor material including a continuous natural fiber and carbon nanofillers is used, said natural fiber being obtained from at least one plant constituent such as a cellulose. A process for manufacturing a continuous carbon fiber from a precursor material, including a step of carbonization of said precursor material, in which the precursor material includes a continuous natural fiber and carbon nanofillers, said natural fiber being obtained from at least one plant constituent, wherein it also includes a step of sizing the precursor material before the carbonization step.