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The fungus Talaromyces fuscoviridis was isolated from soil collected in a copper-mine tailings basin in Pará State, Brazil, an extreme environment that can induce the production of bioactive secondary metabolites. Extracts and fractions obtained after cultivation were analyzed by liquid chromatography coupled to high-resolution mass spectrometry (LC–HRMS) and compared using Global Natural Products Social molecular networking (GNPS), which revealed a family of seven putative polyunsaturated steroids. Isolation led to the characterization of two major steroids: the known Ergosta-3(4),5(6),7(8),14(15),22(23)-pentaene (1a) and a previously unreported metabolite, Ergosta-5(6),7(8),14(15),22(23)-tetraen-3-ol (2a). Their structures were elucidated through comprehensive spectroscopic and spectrometric methods (e.g., UV–Vis, NMR, and high-resolution mass spectrometric [HRMS]), with the structure of steroid 2a being unequivocally confirmed by single-crystal x-ray diffraction (SCXRD). Notably, the biosynthesis of these steroids was significantly enhanced when the cultivation medium was supplemented with manganese chloride (MnCl2). Furthermore, the steroids were tested for their in vitro antioxidant activity against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical using an adapted UHPLC–DAD method, showing over 80% of the scavenging capacity of β-carotene at the lowest tested concentrations.