This study investigated the effect of preharvest treatment of 0.25 mM methyl jasmonate (MeJA) and 0.5 mM salicylic acid (SA) on quality parameters, most important secondary metabolites (lycopene, β-carotene, ascorbic acid, total phenolics, and flavonoids), antioxidant activities, and amino acid contents of ‘Kumato’ tomato. Treatments with MeJA and SA led to an increase of total yield per plant and were effective in maintaining the fruit quality attributes such as firmness, total soluble solids, titratable acidity, and Brix acid ratio at two maturity stages (S1 and S2). In addition, lycopene, β-carotene, ascorbic acid, total phenolics, and flavonoids were significantly higher in the treated fruit than in the control. Moreover, γ-aminobutyric acid (GABA), essential amino acids, and antioxidant activity increased due to MeJA and SA treatments at both stages, especially with MeJA treatment at S2. Overall results also showed the effectiveness of MeJA treatment than SA on improving the yield and nutritional quality of ‘Kumato’ tomato.