Carbon fixation is a critical process for our planet, however, its distribution across the bacterial and archaeal domains of life has not been comprehensively studied. Here, we performed an analysis of 52,515 metagenome-assembled genomes (MAGs) and discover carbon fixation pathways in 1007 bacteria and archaea. We reveal the genomic potential for carbon fixation through the reverse tricarboxylic acid cycle in previously unrecognised archaeal and bacterial phyla (ie. Thermoplasmatota and Elusimicrobiota) and show that the 3-hydroxypropionate bi-cycle is not, as previously thought, restricted to the phylum Chloroflexota. The data also substantially expands the phylogenetic breadth for autotrophy through the dicarboxylate/4-hydroxybutyrate cycle and the Calvin-Benson-Bassham cycle. Finally, the genomic potential for carbon fixation through the 4-hydroxybutyrate/3-hydroxypropionate cycle, previously exclusively found in Archaea, was also detected in the Bacteria. Carbon fixation appears thus to be much more widespread than previously known and this study lays the foundation to better understand the role of archaea and bacteria in global primary production and how they contribute to microbial carbon sinks.