Abstract <p>The demand for natural carotenoids is rising globally as these bioactive compounds are well known for their antioxidant, anti-tumor, anti-diabetic, anti-aging, and anti-inflammatory properties. Cyanobacteria produce carotenoids which play a key role in energy transfer and protection of the photosynthetic apparatus against photooxidative damage. Salinity stress triggers accumulation of carotenoids and other biomolecules in cyanobacteria to counter the stress, but simultaneously limit its growth and productivity. However, metabolic plasticity in several cyanobacteria allows them to improve the growth and productivity by using external carbon sources. Therefore, in the present study, an attempt was made to assess the interactive effect of salinity (0, 5, 15, and 30 g L^–1) and trophic mode of growth (0 and 1 g L^–1 galactose) on growth and biochemical composition of <i>Spirulina</i> sp. CCC540. Addition of NaCl significantly suppressed the growth in a concentration-dependent manner. On the contrary, the carotenoid content increased at lower concentrations of NaCl, the increment was further amplified by addition of galactose. Addition of NaCl (5 g L^–1) under mixotrophic conditions led not only to a 3.50-fold increase in carotenoid production but also to that of other value-added compounds like phycobiliproteins and lipids. An increase in the synthesis of unsaturated fatty acids, linoleic acid, and elaidic acid, and of palmitoleic acid has been recorded. Moreover, an increase in proline content and DPPH activity of the cyanobacterium was also observed as a response to NaCl stress. The results suggest that salt stress under mixotrophic condition can be employed as a potential tool to improve the production of carotenoids and other value-added compounds in <i>Spirulina</i> sp.</p>