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CO2 reduction by combined electro- and bio-catalytic reactions is a promising technology platform for sustainable production of chemicals from CO2 and electricity. While heterogeneous electrocatalysts can reduce CO2 to a variety of organic compounds at relatively high reaction rates, these catalysts have limitations achieving high selectivity for any single product beyond CO. Conversely, microbial CO2 reduction pathways proceed at high selectivity; however, the rates at bio-cathodes using direct electron supply via electricity are commonly limiting. Here we demonstrate the use of non-precious metal cathodes that produce hydrogen in situ to support microbial CO2 reduction to C1 and C2 compounds. CoP, MoS2 and NiMo cathodes perform durable hydrogen evolution under biologically relevant conditions, and the integrated system achieves coulombic efficiencies close to 100% without accumulating hydrogen. Moreover, the one-reactor hybrid platform is successfully used for efficient acetate production from electricity and CO2 by microbes previously reported to be inactive in bioelectrochemical systems. The reduction of CO2 by electro- and biocatalysis offers a promising route to the sustainable production of chemicals and fuels. Here, the integration of methanogenic or homoacetogenic microbes with earth-abundant electrodes allows robust, rapid, and selective CO2 reduction with coulombic efficiencies of up to 100%.