The dicarbofunctionalization of alkenes using organic halides and CO₂ provides a valuable platform for synthesizing carboxylic acids through two C–C bond-forming steps, motifs widely found in pharmaceuticals, agrochemicals, and functional materials. Existing strategies predominantly rely on sequential single-electron transfer (SET) events for substrate activation and carbanion generation, restricting their scope to readily reducible halides. Consequently, many organic halides with highly negative reduction potentials and strong C–X bonds, including electron-rich aryl bromides, aryl chlorides, and alkyl chlorides, remain largely unreactive. Here, we report a visible-light-driven photocatalytic strategy that combines halogen-atom transfer (XAT) and SET processes, where XAT enables generation of carbon-centered radicals from challenging halides, and SET promotes efficient carbanion formation for CO₂ incorporation. This approach enables three-component dicarbofunctionalization of alkenes with a broad range of aryl and alkyl halides, affording carboxylated products in yields of up to 94% across more than fifty examples.