Enzymes that require biotin or lipoic acid prosthetic groups for their activity occur in all domains of life and play essential roles in metabolism. The biotin prosthetic group participates in carboxylation reactions by transferring CO₂ to substrates in processes like gluconeogenesis and fatty acid synthesis. Lipoic acid is a redox-active prosthetic group for the oxidative decarboxylation of α-oxoacids by multienzyme complexes like pyruvate dehydrogenase. The de novo synthesis of these vitamins depends on the production of fatty acid precursors and has been most extensively characterized in Escherichia coli and Bacillus species. The octanoyl-acyl carrier protein precursor for lipoic acid is synthesized in reactions catalyzed by the fatty acid biosynthesis (Fab) enzymes. The octanoyl moiety is linked to the lipoyl domains of lipoic acid-dependent enzymes and then converted to lipoate by lipoyl synthase. For biotin biosynthesis, different bacterial species have adopted the BioC-BioH, BioI-BioW, or BioZ pathways that use different combinations of Fab enzymes to produce the pimeloyl-acyl carrier protein or pimeloyl-CoA intermediate of the pathway. Ring-closure enzymes convert the pimeloyl thioesters to biotin, which is ligated to target enzymes by a biotin protein ligase. This chapter offers a current overview of the role of fatty acid metabolism in biotin and lipoic acid biosynthesis.