Recent climate changes worldwide have negatively impacted crop yields, highlighting the urgent need to develop new cultivation strategies to counteract this phenomenon. Our study aimed to analyze the effects of saline (0 mM, 100 mM, 200 mM, and 300 mM NaCl) and heat stress (24 °C and 32 °C) on the physiological parameters of Chenopodium quinoa variety “Regalona,” evaluating the efficacy of the microalgal biostimulant Chlorella vulgaris-like extract (0%, 0.025% and 0.05%). Sprouts grown under these different conditions were assessed for antioxidant content, antioxidant activity, reactive oxygen species, and photosynthetic pigments. The analyses did not reveal significant effects of the two microalgal concentrations on germination percentage or sprout length across the various temperature and salinity conditions. However, antioxidant activity was increased in many experimental trials, especially when the microalgae were combined with salt stress, with the higher biostimulant concentration showing more pronounced effects. Conversely, a temperature of 32 °C negatively impacted the parameters measured. These findings provide a basis for further research aimed at enhancing the antioxidant and nutraceutical properties of plants valuable for human nutrition.