Nitric oxide is an important signalling molecule which is involved in many different physiological processes in plants. Here we report about a NO-fixing mechanism in Arabidopsis, which allows the fixation of atmospheric NO into nitrogen metabolism. We fumigated Arabidopsis plants cultivated in soil or as hydroponic cultures during the whole growing period with up to 3 ppmv of NO gas. Transcriptomic, proteomic and metabolomic analyses were used to identify non-symbiotic hemoglobin proteins as key components of the NO-fixing process. Overexpressing non-symbiotic hemoglobin 1 or 2 genes resulted in four-fold higher nitrate levels in these plants compared to NO-treated wild-type. Correspondingly, rosettes size and weight, vegetative shoot thickness and seed yield were 25%, 40%, 30%, and 50% higher, respectively, than in wild-type plants. Fumigation with 250 ppbv (15) NO confirmed the importance of non-symbiotic hemoglobin 1 and 2 for the NO-fixation pathway and we calculated a daily uptake for non-symbiotic hemoglobin 2 overexpressing plants of 250 mg N/kg dry weight. This mechanism is probably important under conditions with limited N supply via the soil. Moreover, the plant-based NO uptake lowers the concentration of insanitary atmospheric NOx and in this context NO-fixation can be beneficial to air quality.