Ammonia (NH₃) is a promising carbon-free fuel for future energy systems due to its high energy density and ease of storage and transportation. However, its practical applications are currently limited by significant challenges such as high ignition energy and low burning velocity, resulting in difficult ignition and unstable combustion. Improving the ignition and combustion behaviours of NH₃/air mixtures is essential to enable reliable, high-efficiency operation. This study proposes and examines a two-stage, single-device nanosecond surface dielectric barrier discharge (nSDBD) strategy coupling plasma-assisted NH₃ reforming (PAAR) with plasma-assisted NH₃ combustion (PAAC). Experiments were conducted in a constant volume chamber (CVC) and complemented by a zero-dimensional model for mechanistic interpretation. The discharge parameters of direct nSDBD ignition was first optimised, followed by a quantification of the effects of ignition discharge parameters, operating conditions (equivalence ratio, initial pressure, initial temperature), and discharge configurations. Finally, a joint optimisation of reforming parameters and ignition parameters for the proposed two-stage single-device strategy was performed. PAAR seeds a reactive reservoir including H₂ at approximately 0.1% of the mixture. Compared with direct ignition, the two-stage PAAR–coupled PAAC strategy achieves higher supplied energy, faster ignition, and more intense combustion. Simulations agree with experiments and elucidate the key radical pools and reaction pathways responsible for reforming-enabled ignition facilitation and combustion enhancement. This research delivers practical parameter windows and device guidelines, supporting compact nSDBD implementation for robust NH₃ ignition and utilisation.