Cyanobacteria can play an important role in sustainable agriculture by improving crop growth and production, as well as environmental quality. The current study was conducted to evaluate the role of Spirulina platensis extract in the improvement of growth, photosynthetic capacity and yield of Lupinus luteus. Different concentrations (0.25, 0.5 and 1.0%) of S. platensis methanolic extract were used for priming seeds and foliar spraying applications. Growth, photosynthetic pigment content and activity were recorded at 35 days of cultivation. The yield measurements and protein profile of seeds were performed at 60 days. For both treatments, the lower concentration (0.25%) of the extract was the most successful in improving all growth metrics and the phytohormonal level of L. luteus. Photosynthetic pigment and capacity, nutrient content and yield components of L. luteus were improved with the extract of 0.25% concentration. However, the growth was significantly inhibited at the higher concentration (1.0%), recording lower values of the measured characters than the control. A positive correlation was observed between the total chlorophyll, photosynthetic rate, yield parameters and carbohydrate accumulation by the application of the S. platensis extracts. The protein profile of seeds revealed that spraying treatment triggered the appearance of a new band of 30.56 KDa. The promotion of growth could be attributed to the nutrients, bioactive molecules and phytohormones in the extract. The use of Spirulina-based stimulators is reliable with the concept of sustainable agriculture by enhancing photosynthetic pigment content and rate ensuring the correlation between the yield and those measured parameters of L. luteus.