Involved in coproporphyrin-dependent heme b biosynthesis. Catalyzes the insertion of ferrous iron into coproporphyrin III to form Fe-coproporphyrin III. Fe-coproporphyrin III + 2 H(+) = coproporphyrin III + Fe(2+) Porphyrin-containing compound metabolism; protoheme biosynthesis. Belongs to the ferrochelatase family.