An experiment was conducted to investigate the effects of water deficit stress (field capacity (FC), 50%, and 30% of FC) and foliar application of gamma-aminobutyric acid (GABA) and spermidine (control and 3 mg L⁻¹), as well as their combined application, on growth and selected physiological traits of basil. The highest plant biomass was observed under irrigation at FC + simultaneous foliar application of spermidine and GABA. The main effects of water deficit and foliar treatments significantly influenced chlorophyll, H2O2, malondialdehyde, proline, elemental content, and essential oil content of the plant. The highest chlorophyll a, calcium, magnesium, phosphorus, and potassium content were observed under irrigation at FC. Irrigation at FC and 50% FC significantly increased chlorophyll b and nitrogen contents. Irrigation at 30% FC resulted in elevated levels of H2O2, malondialdehyde, and proline accumulation. All three foliar treatments led to increased chlorophyll b, nitrogen and potassium contents. Simultaneous foliar application of both compounds contributed to a reduction in H2O2 and malondialdehyde levels, while enhancing chlorophyll a, proline, phenolic compounds, calcium, magnesium, phosphorus, and essential oil contents. Essential oil content was notably increased under irrigation at 50% FC. Sixteen constituents were identified in the basil essential oil, with methyl chavicol (38.42–42.38%) being the predominant compound, particularly prominent in the treatment combining irrigation at 30% FC with foliar application of both compounds. The results of the present study demonstrate the positive effect of concurrent application of both compounds on the evaluated physiological and biochemical traits of basil under water deficit conditions.