Involved in coproporphyrin-dependent heme b biosynthesis (PubMed:25908396). Catalyzes the insertion of ferrous iron into coproporphyrin III to form Fe-coproporphyrin III (PubMed:25908396). It can also insert iron into protoporphyrin IX, but it has a much stronger preference for coproprophyrin III as the substrate (PubMed:25908396). Fe-coproporphyrin III + 2 H(+) = coproporphyrin III + Fe(2+) kcat is 165 min(-1) with coproporphyrin III as substrate. kcat is 15 min(-1) with protoporphyrin IX as substrate. Porphyrin-containing compound metabolism; protoheme biosynthesis. Mutant accumulates coproporphyrin III. Belongs to the ferrochelatase family.