The magnetism-induced symmetry breaking in photoelectron diffraction patterns of 2_p3/2 photoelectrons from a ferromagnetic Fe(001) single crystal surface is studied experimentally and theoretically. Two-dimensional photoelectron intensity angular distribution patterns were recorded at 1193 eV photon energy for both helicities of the circularly polarized light and for opposite magnetization directions of the sample by a display-type spherical mirror analyzer, which allows simultaneous energy and momentum analysis of emitted photoelectrons. The macroscopic magnetization of the sample induces an additional symmetry breaking in the circular dichroism of the Fe _p3/2 photoelectron angular distribution patterns which is related to the presence of magnetic moments on the Fe atoms. Multiple-scattering cluster photoelectron diffraction calculations agree well with experiment, and reproduce even fine details of the observed photoelectron diffraction features. The details of that breaking of mirror symmetry of photoelectron scattering in the plane spanned by light incidence and electron emission due to the presence of a magnetization within that plane depends both on the structure and the magnetism of the sample. In connection with multiple scattering calculations, measurements of the magnetism-induced symmetry breaking by two-dimensional photoelectron diffraction patterns may thus be used as a powerful tool for simultaneous structural and magnetic investigations of single crystalline magnetic samples and ultrathin films.