Recently published work has underlined the importance of longwave radiative heating in the formation of tropical cyclones; however, its effect on midlatitude eddies is less clear. Using the GFDL High-Resolution Atmospheric Model (HiRAM), we perform a mechanism-denial experiment in which the radiative cooling profile at each model time step is overwritten with the climatological mean, computed from a control simulation. This approach separates the mean and transient effects of radiative heating on the extratropical circulation. We find that, when radiative cooling is fixed, the globally-averaged eddy kinetic energy is enhanced by ~5%. We show that radiative cooling near the cloud top in baroclinic eddies weakens the horizontal temperature gradient and reduces the generation of eddy available potential energy, the precursor to eddy kinetic energy. Overall our results indicate that, while radiative interactions promote the formation of tropical cyclones, they inhibit eddy activity in the extratropics.