It has been accepted dogma that eukaryotes and heme-synthesizing bacteria use the same metabolic intermediates in their heme synthesis pathways, where protoporphyrin is the final intermediate into which iron is inserted to make protoheme. Herein, we present data demonstrating that Gram-positive bacteria do not use protoporphyrin as an intermediate but, instead, have an altered set of terminal reactions that oxidize coproporphyrinogen to coproporphyrin and insert ferrous iron into coproporphyrin, resulting in the formation of coproheme. A newly characterized enzyme, HemQ, decarboxylates coproheme to generate protoheme. Because some organisms that possess this coproporphyrin-dependent branch are major causes of human disease, HemQ is a novel pharmacological target of significant therapeutic relevance, particularly given high rates of antimicrobial resistance among these pathogens.