Basic metal industries, like that of steel and copper, provide essential high quality and recyclable products for the infrastructure and technology development towards a carbon neutral society. The reliance of the human wellbeing on these metals has led to a 21% increase of the steel demand in the last decade, and it is expected to triple the copper demand from 2010 to 2050. However, the steel and copper production industries are today excessively dependent on the utilization of fossil fuels, either as a process heat source by combustion or as a chemical feedstock. Guaranteeing the sustainable supply of steel and copper products in the future demands a systemic change of the entire value chains of these industries. This study explores the potential of hydrogen gas as a reducing agent to replace the carbonaceous substances currently used in key metallurgical processes of the copper production and steel by-product valorisation, aiming at reducing the process-related CO2 emissions. Samples of steelmaking by-products, like slag and rolling mill scale, and of blister copper from real industrial operations were prepared and subjected to controlled thermal cycles in the presence of hydrogen-based atmospheres. Then, a thorough compositional and structure characterization was performed on the resulting metallurgical product. The hydrogen-based experiments were combined with thermodynamic calculations in order to gain insight into the physico-chemical aspects of the reactions occurring during blister copper refining (Cu-O-S-H system) and during the iron oxide reduction of slag and mill scale mixtures (Fe-O-H-X systems, where X= Si, Mg, Ca, Al). The results of this study will allow us to build a fundamental basis for the development of the hydrogen-based technology needed to reduce the CO2 emissions from the established process metallurgy and by-product valorisation routes.