Light–matter interactions are often considered to be mediated by the electric component of light only, neglecting the magnetic contribution. However, the electromagnetic energy density is equally distributed between both parts of the optical fields. Within this scope, we experimentally demonstrate here, in excellent agreement with numerical simulations, that plasmonic nanostructures can selectively manipulate and tune the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement or decay of magnetic and electric emission from trivalent europium-doped nanoparticles in the vicinity of plasmonic nanocavities, designed to efficiently couple to either the electric or magnetic emission of the quantum emitter. Specifically, by precisely controlling the spatial position of the emitter with respect to our plasmonic nanostructures, by means of a near-field optical microscope, we record local distributions of both magnetic and electric radiative local densities of states (LDOS) with nanoscale precision. The distribution of the radiative LDOS reveals the modification of both the magnetic and electric optical quantum environments induced by the presence of the metallic nanocavities. This manipulation and enhancement of magnetic light–matter interaction by means of plasmonic nanostructures opens up new possibilities for the research fields of optoelectronics, chiral optics, nonlinear and nano-optics, spintronics, and metamaterials, among others.