Catalyzes the sequential decarboxylation of the four acetate side chains of uroporphyrinogen to form coproporphyrinogen and participates in the fifth step in the heme biosynthetic pathway (PubMed:11069625, PubMed:11719352, PubMed:14633982, PubMed:18004775, PubMed:21668429). Isomer I or isomer III of uroporphyrinogen may serve as substrate, but only coproporphyrinogen III can ultimately be converted to heme (PubMed:11069625, PubMed:11719352, PubMed:14633982, PubMed:21668429). In vitro also decarboxylates pentacarboxylate porphyrinogen I (PubMed:12071824).