The decarbonization of energy-intensive industrial sectors requires the implementation of low-carbon fuels and advanced combustion technologies. This study investigates the co-combustion of hydrogen and natural gas in an industrial diffusion burner, with particular emphasis on pollutant emissions and heat transfer. Experimental investigations and theoretical analyses were conducted for fuel blends containing up to 60 vol.% hydrogen over a broad range of operating conditions. A modified burner incorporating staged combustion air, with primary and secondary air supplied separately, was tested in a semi-industrial combustion chamber under high-temperature conditions. The results showed that hydrogen addition increased the total heat flux by up to 3.5 %, primarily because of the higher combustion and flue-gas temperatures and changes in the radiative properties of the combustion products, particularly CO₂ and H₂O. However, the higher oxidation rate of hydrogen reduced the flame length, partially limiting radiative heat transfer directly from the flame. Experimental evaluation of the proposed combustion strategy confirmed stable burner operation with very low carbon monoxide emissions, typically not exceeding a few ppm, even at high secondary air ratios. Although hydrogen enrichment initially increased NO emissions, the application of air staging significantly suppressed NO formation, achieving reductions of more than 55 % at a secondary air ratio of 0.5. The emission-reduction strategy was more effective at lower excess-air ratios. Overall, the results demonstrate that hydrogen–natural gas co-combustion in industrial furnaces is feasible and can maintain NO emissions below 50 ppm under the investigated operating conditions without requiring secondary flue-gas treatment technologies. The proposed approach therefore represents a promising pathway for the decarbonization of high-temperature industrial processes.