As the most important source of commodity grain in China, Northeast China plays a crucial role in guaranteeing national food security. The application of biochar in agricultural ecosystems has shown immense potential in ensuring crop yields while mitigating N₂O emissions. However, the long-term impacts and mechanisms of successive application of corn stover and its derived biochar on soil N₂O emission in the corn monocropping region, such as Northeast China, remain unclear. A five-year field experiment was conducted in Northeast China to fill this research gap regarding the soil nitrogen (N) cycle. Three experimental treatments were established: a control with no corn stover or biochar application (CK), corn stover returned yearly at a rate of 7.5 t ha⁻¹ (ST), and biochar added yearly at a rate of 2.6 t ha⁻¹ (BC) corresponding to 35% of the stover addition rate in ST. Identical mineral fertilizers were applied in all three treatments. The total accumulated N₂O emissions across five analyzed growing seasons within the CK, ST, and BC treatments were 260.2, 184.0, and 151.0 mg N₂O m⁻², respectively, with significant 29.3% and 42.0% decreases observed in ST and BC treatments, respectively, compared with the control. Based on the annual average from 2013 to 2017, ST and BC treatments significantly increased soil pH and total N (TN) content and significantly decreased the levels of NO₃^––N, NH₄⁺-N, and soil bulk density (BD). Additionally, BC treatment remarkably lowered the average NH₄⁺-N content than that under ST treatment by 24.1%. Both ST and BC showed a significant inhibitory effect on nitrate reductase (NR), nitrite reductase (NiR), and hydroxylamine reductase (HyR) activities related to denitrification. Soil N₂O emission was significantly positively correlated with BD, NO₃^–-N, NH₄⁺-N, NR, NiR, and HyR activities. Path analysis suggested that N₂O emissions were primarily driven by NR and HyR activities and NO₃^–-N content. Overall, the applications of corn stover and its derived biochar are a feasible means of mitigating soil N₂O emissions in the context of continuous corn cropping systems in mid-latitude regions like Northeast China, with biochar being more beneficial than stover application.