Microalgae are photosynthetic cell factories that can be used for the production of biofuel. However, lower biomass and lipid productivity are major limitations for their large-scale applications. The present study explores use of exogenous seaweed extract for enhancement of biomass and lipid content in microalgae. The addition of 1% v/v seaweed extract resulted in a biomass yield of 304 mg/L, which is higher than the BG-11 grown culture. Furthermore, it was observed that the addition of seaweed extract under nutrient stress conditions resulted in stress mitigation as well as enhancement in biomass production. Specifically, the addition of seaweed extract under nitrogen starvation resulted in nearly two-fold higher biomass with 43% lipid content. Similarly, seaweed extract addition under salinity stress conditions, resulted in approximately 1.8-fold higher biomass than the control culture. Further, metabolomics analysis revealed that the exogenous addition of seaweed extract enhances the concentration of key metabolites, thereby mitigating stress tolerance. This study highlights the potential application of exogenous seaweed extract as an economic and practical growth modulator for improving both biomass and biofuel production potential in microalgae.