Display omitted •Compared to other steel slags, LD-slag suppressed CH4 production in a paddy soil.•LD-slag amendment mitigated CH4 emissions by 17.8–24.0% in submerged paddies.•LD-slag amendment decreased inorganic As concentrations in rice grain by 18.3–19.6%.•LD-slag amendment increased grain yield by 10.3–15.2%. Over the past decades, with increasing steel manufacturing, the huge amount of by-products (slags) generated need to be reused in an efficient way not only to reduce landfill slag sites but also for sustainable and eco-friendly agriculture. Our preliminary laboratory study revealed that compared to blast furnace slag, electric arc furnace slag and ladle furnace slag, the Linz-Donawitz converter (LD) slag markedly decreased CH4 production rate and increased microbial activity. In the greenhouse experiment, the LD slag amendment (2.0 Mg ha−1) significantly (p < 0.05) increased grain yield by 10.3–15.2%, reduced CH4 emissions by 17.8–24.0%, and decreased inorganic As concentrations in grain by 18.3–19.6%, compared to the unamended control. The increase in yield is attributed to the increased photosynthetic rates and increased availability of nutrients to the rice plant. Whereas, the decrease in CH4 emissions could be due to the higher Fe availability in the slag amended soil, which acted as an alternate electron acceptor, thereby, suppressed CH4 emissions. The more Fe-plaque formation which could adsorb more As and the competitive inhibition of As uptake with higher availability of Si could be the reason for the decrease in As uptake by rice cultivated with LD slag amendment.