Non-radiative transfer processes are often regarded as loss channels for an optical emitter1 because they are inherently difficult to access experimentally. Recently, it has been shown that emitters, such as fluorophores and nitrogen-vacancy centres in diamond, can exhibit a strong non-radiative energy transfer to graphene2–6. So far, the energy of the transferred electronic excitations has been considered to be lost within the electron bath of the graphene. Here we demonstrate that the transferred excitations can be read out by detecting corresponding currents with a picosecond time resolution7,8. We detect electronically the spin of nitrogen-vacancy centres in diamond and control the non-radiative transfer to graphene by electron spin resonance. Our results open the avenue for incorporating nitrogen-vacancy centres into ultrafast electronic circuits and for harvesting non-radiative transfer processes electronically.