Nonthermal plasma (NTP) presents a promising pathway for sustainable ammonia synthesis under mild conditions, enabling activation of nitrogen without the need for high thermal input. While most studies to date have focused on plasma ammonia synthesis under ambient pressure, the potential benefits of elevated pressure, such as improved thermodynamic favorability and enhanced compatibility with downstream ammonia separation technologies, remain underexplored. In this work, we investigate plasma-driven ammonia synthesis under elevated pressure by combining experimental measurements with detailed plasma chemical kinetics modeling. A dielectric barrier discharge plasma reactor was employed, with the system pressure controlled up to 3 bar using a high-pressure regulator. Contrary to thermodynamic expectations, the experimental results reveal that increasing pressure suppresses ammonia yield in the plasma environment, primarily due to a reduction in the reduced electric field (E/N), which diminishes the energy of electrons available for molecule activation. The underlying reaction mechanism was elucidated using in situ optical diagnostics and chemical kinetics simulations. Path flux analysis confirms that N2 is dissociated by energetic electrons into N and excited N-(2D) species, which are subsequently hydrogenated to form NH and NH2 radicals. These intermediates recombine via NH2 + H-(+M) → NH3(+M) and NH + H2 + M → NH3 + M to form ammonia. Notably, elevated pressure does not alter the dominant reaction pathways but significantly influences the reaction rates and plasma characteristics. Sensitivity analysis highlights that the electron-impact dissociation of N2 [e + N2 → e + N + N-(2D)] is the rate-limiting step and has the greatest promoting effect on ammonia formation. These insights offer guidance for optimizing plasma operating conditions and advancing the practical application of plasma-assisted ammonia synthesis under pressurized conditions. While most studies to date have focused on plasma ammonia synthesis under ambient pressure, the potential benefits of elevated pressure, such as improved thermodynamic favorability and enhanced compatibility with downstream ammonia separation technologies, remain underexplored. In this work, we investigate plasma-driven ammonia synthesis under elevated pressure by combining experimental measurements with detailed plasma chemical kinetics modeling. A dielectric barrier discharge plasma reactor was employed, with the system pressure controlled up to 3 bar using a high-pressure regulator. Contrary to thermodynamic expectations, the experimental results reveal that increasing pressure suppresses ammonia yield in the plasma environment, primarily due to a reduction in the reduced electric field (E/N), which diminishes the energy of electrons available for molecule activation. The underlying reaction mechanism was elucidated using in situ optical diagnostics and chemical kinetics simulations. Path flux analysis confirms that N 2 is dissociated by energetic electrons into N and excited N­( 2 D) species, which are subsequently hydrogenated to form NH and NH 2 radicals. These intermediates recombine via NH 2 + H­(+M) → NH 3 (+M) and NH + H 2 + M → NH 3 + M to form ammonia. Despite these compelling advantages, the fundamental understanding of plasma-driven ammonia synthesis under elevated pressures remains limited. This is partly due to the experimental complexity and plasma instabilities associated with high-pressure operation. To address this gap, we investigate an NTP-driven ammonia synthesis from N 2 and H 2 at pressures up to 3 bar. Through a combination of in situ optical diagnostics and plasma chemical kinetic modeling, we elucidate the pressure-dependent reaction pathways and identify key rate-limiting steps. A comprehensive mechanism is proposed, with emphasis on pressure-adaptive chemistry and intermediate species evolution. The flow rates of N 2 and H 2 were controlled by mass flow controllers (Bronkhorst, F-201CV), and the gases were thoroughly mixed at a fixed total flow rate of 40 mL/min with an N 2 /H 2 ratio of 1:3 before entering the DBD reactor. This stoichiometric ratio was chosen based on thermodynamic equilibrium and plasma reaction kinetics considerations, ensuring sufficient hydrogen availability for nitrogen hydrogenation. The reactor pressure was controlled using a high-pressure regulator (Festo, MS2-LR), allowing adjustment in 1 bar increments within the range of 1–3 bar. Further details are provided in Section S1 . As a result, the energy flux allocated to H 2 dissociation weakens, while the electron energy directed toward N 2 vibrational excitation correspondingly intensifies. This inverse Consequently, the thermodynamic gains from increased pressure are outweighed by kinetic losses. Furthermore, the energy yield decreased with increasing discharge power at all tested pressures, primarily because the excess electrons generated at higher discharge power fail to effectively collide with target molecules (N 2 and H 2 ). Plasma chemical kinetics modeling confirms that NTP-driven ammonia synthesis proceeds via the same reaction mechanism across a pressures range of 1–3 bar. The kinetic modeling results indicate that N 2 is initially dissociated by electrons to produce atomic N and N­( 2 D) or excited through collisions to generate N 2 (A 3 ). First, incorporating a suitable catalyst could lower the activation energy for NN triple-bond dissociation, thereby enhancing reaction kinetics and increasing ammonia yield. Second, the use of nanosecond-pulsed-discharge-driven DBD may generate intense electric fields on nanosecond time scales, efficiently promoting N 2 dissociation while minimizing thermal effects, ultimately shifting the thermodynamic equilibrium toward ammonia formation. Finally, the limited availability of in situ diagnostics restricts experimental validation of intermediate species and mechanistic pathways.