Candidatus Magnetoglobus multicellularis is a spherical, multicellular, magnetotactic prokaryote (MMP) composed of 10–40 genetically-identical, Gram-negative cells. It is known that monochromatic light of low intensity influences its average swimming velocity, being higher for red light (628 nm) and lower for green light (517 nm). In this study, we determined the effect of light of different wavelengths and intensities on the swimming velocity of Ca. Magnetoglobus multicellularis under different magnetic field intensities. The swimming velocities of several organisms exposed to blue light (469 nm), green light (517 nm) and red light (628 nm) with intensities ranging from 0.36 to 3.68 Wm−2 were recorded under magnetic field intensities ranging from 0.26 to 1.47 Oe. Our results showed that MMPs exposed to green light display consistently lower average swimming velocities compared to other wavelengths of light. We also show for the first time that photokinesis in Ca. Magnetoglobus multicellularis is dependent on the magnetic field being applied. The relationship between light wavelength and intensity and magnetic field strength and swimming velocity in this MMP is therefore complex. Although the mechanism for the observed behaviour is not completely understood, a flavin-containing chromophore may be involved.