A decarboxylative ring-opening protocol of cyclic tertiary carboxylic acids via iron-catalyzed photoinduced ligand-to-metal charge transfer (LMCT) is described. This reaction enables the preparation of 1,n-dicarbonyl compounds through the homolytic C–C bond cleavage of unstrained carbocyclic and heterocyclic ring systems. This method exhibits a lot of synthetic advantages including mild conditions, simple operation, and convenience of amplification. Mechanistic studies support the generation of peroxy radical species via oxygen capture followed by radical fragmentation.