Thioesters are important in synthesis, materials science, and biology, and their preparation traditionally relies on the use of disagreeable thiols. Here, we report a thiol-free protocol that stitches together widespread carboxylic acids and aryl halides, producing a diverse array of thioesters. Crucial to this strategy is the discovery that tetramethylthiourea can serve as both a sulfur source and, upon direct excitation by purple light, as a strong reductant, suitable for activating aryl halides via single-electron transfer. Coupling of the resulting aryl radicals provides an isothiouronium ion intermediate, which can be attacked by carboxylic acids via a polar pathway, affording the thioester products under mild conditions. A photochemical method for synthesizing thioesters from readily available aryl halides and carboxylic acids is here disclosed. This thiol-free protocol hinges on the direct excitation of 1,1,3,3-tetramethylthiourea and its multifaceted ability to act as the sulfur source, generate aryl radicals upon SET activation of halides, and trap them to in situ produce reactive isothiouronium ions. image