Pyrolytic carbon that exhibits negative magnetoresistance is irradiated with 2 MeV electrons at temperatures below 35 K, and the changes in electronic transport properties such as zero-magnetic field resistivity, Hall coefficient, and magnetoresistance are measured as a function of electron fluence. With increasing electron fluence, the zero-field resistivity decreases, while the Hall coefficient and the absolute values of negative magnetoresistance increase. The experimental data are analyzed assuming that the densities of electrons and holes vary with the magnetic field. The analysis shows that the densities increase with the square of the magnetic field; the result is in good agreement with the Bright theory, in which the two-dimensional Landau levels are assumed to be broadened due to defect scattering. Both intrinsic defects and irradiation-produced defects act as electron acceptors. The addition of acceptors increases the ratio of hole density to electron density, $p/n,$ resulting in the enhancement of negative magnetoresistance. The present results clarify that the negative magnetoresistance in pyrolytic carbon is caused by the existence of acceptor defects and the two-dimensional Landau levels, which are broadened by the defects. In addition, they suggest that the intrinsic acceptor defects in pyrolytic carbon are presumably vacancies.