Quasiparticles arising from the interaction between mobile impurities and a quantum many-body environment—known as polarons—play a pivotal role in shaping the optical and electronic properties of low-dimensional systems. Here, we report the direct observation of electrically generated polaron-polaritons within a monolayer molybdenum diselenide microcavity. By embedding the monolayer in a planar optical cavity, we achieve strong coupling between exciton-polarons and cavity photons, creating an electrically driven light-emitting diode based on polaron-polaritons. The device exhibits an external quantum efficiency of ∼0.15%, representing a 10-fold enhancement over prior exciton-polariton devices based on monolayer tungsten disulfide. This demonstration establishes a versatile platform for inversionless laser technology and for polariton-based quantum optoelectronics while offering insights into radiative many-body physics in two-dimensional semiconductors.