Cavity quantum electrodynamics (CQED) represents one of the most fascinating systems for the study of quantum physics. Solid-state CQED systems based on semiconductor micro-cavities coupled to single quantum dots (QDs) are particularly interesting for their potential scalability and integrability. However, the progress in semiconductor CQED has so far been hampered by the very limited degree of control, due to the ultrafast picosecond time scale and subwavelength spatial scale, which make the control of the QD-photon interaction in real time extremely challenging. Recently, we have proposed and demonstrated an ultrafast, non-local control scheme based on the coupling of a control cavity to a target cavity containing QD emitters. By injecting free carriers into the control cavity, the electric field distribution in the coupled-cavity system can be modified, resulting in real-time shaping of vacuum field at the target cavity without directly perturbing the emitter’s coherent evolution. The QD-cavity interaction rate and the spontaneous emission rate are manipulated on a timescale of ~200 ps, well below the radiative lifetime. This opens the way to the real-time control of semiconductor CQED and towards a novel form of photonic devices for ultrafast lasing pulse generation.