The hydrogenation of carbon dioxide offers a large range of possible reactions for converting hydrogen to chemical compounds that can be easily stored, transported and used as fuels or platform molecules. In this study, CO2 hydrogenation was biocatalysed by multispecies microbial communities to produce formate, butyrate and acetate. A hybrid metal/microbial catalysis was pointed out in the presence of iron. Addition of FeCl3 10 mM increased the production of acetate by 265% and butyrate by 73%, to 5.26 and 14.19 g/L, respectively. A stable acetate production rate of 830 mg/L/d was thus sustained for more than 20 days. The presence of iron promoted the selection of Firmicutes and the best performances were linked to the growth of a restricted number of dominant species of two genera: Clostridium and Megasphaera. Various possible catalysis mechanisms are discussed and guidelines are proposed for further development and scale-up of the process.