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Photoinducible proximity labeling (PL) using photocatalysts offers high spatiotemporal resolution for profiling protein–protein interactions (PPIs). Conventional approaches require genetic installation of a tag to tether the photocatalyst to a protein of interest (POI), which may perturb native protein function and cause artificial labeling. Ligand-directed delivery of photocatalysts to native POIs has emerged as a tag-free alternative; however, this strategy suffers from nonspecific labeling by unbound catalysts and an inherent washing dilemma, where insufficient washing leads to background labeling while excessive washing disrupts ligand binding. These limitations have severely restricted tagfree, ligand-directed PPI profiling. Herein, we report a switchable photoinducible PL strategy based on a nitrobenzoxadiazole (NBD) unit that becomes catalytically active only after covalent conjugation to a POI. This approach consists of a two-step process: introduction of an N-NBD moiety into the POI using a catalytically inactive O-NBD unit, followed by light-induced PL catalyzed by N-NBD. Model experiments identified N-methyl luminol as a selective labeling reagent activated by N-NBD. Using a biotin-conjugated O-NBD unit as a catalytically inactive precursor, biotinconjugated protein A was selectively labeled as a PPI partner of streptavidin. This switchable PL method circumvents the washing dilemma, suppresses nonspecific labeling, and enables high-resolution, tag-free proteomic analyses.