Addition of phytohormones (diethyl aminoethyl hexanoate and indole acetic acid) at 10−5 M significantly increased the growth of a green microalga, Chlorella pyrenoidosa up to 62.25% achieving cell concentrations of 5.13╳107 cells ml−1. Yielding of high-value added byproducts (pigments, carbohydrate, proteins, and fatty acids) was more in presence of phytohormones comparing to the control. Further transcriptomics analysis demonstrated phytohormones upregulated numerous genes involved in DNA replication and repair pathways, and energy metabolisms (glycolysis, citrate cycle, and oxidative phosphorylation). Moreover, genes in purine metabolism, and porphyrin and chlorophyll metabolism were also more expressed by up to 6.49 times with phytohormones. These pathways can supply more cellular signaling molecules and antioxidant contents. This study carried new insights on the key driving factors in phytohormone enhanced microalgal biomass production processes, which can help to find more feasible application solutions of phytohormones in microalgal biofactories. Display omitted •Microalgal biomass production was enhanced by 62.25% under phytohormones.•High-value added byproducts yields more with addition of phytohormones.•Improved DNA replication and repair processes helped to more cells' production.•Genes involved in energy metabolism were significantly upregulated with phytohormones.