Nitrogen (N) is a key nutrient that significantly affects yield and grain protein content in malting barley. However, excessive N fertilization contributes substantially to total greenhouse gas (GHG) emissions. To align malting barley cultivation with the European Green Deal, it is essential to reduce N inputs while maintaining high productivity and grain quality. Biostimulants derived from Ascophyllum nodosum extract (ANE) have been shown to improve soil N uptake and enhance nitrogen use efficiency. To evaluate their agronomic and environmental impact, field trials were conducted in Almyros, Greece, during the 2022–2023 and 2023–2024 growing seasons using two malting barley genotypes: a commercial variety (Fortuna) and a genotype (G62) with a different growth cycle. Five fertilization treatments were applied: i) sulfur-coated urea at 90 kg N/ha (U), ii) U + ANE (U + B), iii) urea with urease inhibitor at 75 kg N/ha (UI), iv) UI + ANE (UI + B), and v) an unfertilized control (C). Applications of ANE were carried out at Zadoks’ stages Z*24–30 and for surface fertilization at Z*30–33 for Fortuna and G62, respectively. The UI + B treatment significantly increased aboveground biomass and grain yield—by 50.72% and 53.23% in the first year, and 75.25% and 70.99% in the second—compared to the control. For G62, U + B proved more effective, enhancing biomass and yield by up to 55.67% and 78.75%, respectively. In terms of carbon footprint, UI + B resulted in a maximum reduction of 48.3% and 36.9% CO₂-eq per kg of yield for Fortuna, and 27.2% and 18.9% CO₂-eq per kg for G62, across the two consecutive seasons. In conclusion, the combined use of ANE with reduced N fertilization and urease inhibitors can improve yield and nitrogen efficiency while significantly lowering the carbon footprint of malting barley cultivation.