Illuminating results: Activation of non‐emissive [AuIII(N N N)(NHC)] complexes (such as 1) through reduction by intracellular glutathione gives active AuI–NHC complexes, which show promising anti‐cancer properties, accompanied by release of the highly fluorescent ligand. The high fluorescence “switch‐on” efficiency makes these AuIII complexes excellent probes for cellular thiol detection.