Drought stress cripples crop productivity, especially in arid and semi-arid regions. This study explored the impact of selenium (Se) application on the growth and yield of quinoa under control and drought stress. A pot trial was conducted to improve quinoa's drought tolerance through Se seed priming (6 mg Se L-1) and foliar application (15 mg L-1). Plants were subjected to drought at multiple leaf, flowering, and grain filling stages. Drought significantly reduced the growth, yield, physio-biochemical and quality attributes of quinoa, while Se application (seed priming and foliar spray) improved drought tolerance and productivity by sustaining plant water status. Se application (15 mg L-1 foliar spray) enhanced the growth and yield parameters, leaf chlorophyll contents (8.13%), total phenolics (5.95%), water use efficiency (12%), water relations [(leaf relative water contents (7.08%), osmotic potential (5.13%), water potential (13.53%), and turgor potential (16.27%)], biological yield (7.74%), grain yield (12.12%), and grain protein contents (2.85%) under drought stress. Drought stress imposed at the grain-filling stage proved most detrimental for quinoa. Se foliar application (15 mg L-1) significantly mitigated adverse effects of drought by improving the antioxidant defense mechanism, i.e. superoxide dismutase (33.71%), peroxidase (35.34%), catalase (21.15%), and glutathione peroxidase (35.08%). The highest yields were recorded with 15 mg L-1 Se foliar spray under full irrigation, while the lowest occurred in untreated drought-stressed plants. This study highlights the potential of Se in alleviating drought stress in quinoa, improving yield and nutritional quality, and providing valuable insights for sustainable quinoa production in drought-prone environments.