Quality of fresh produce is the most critical issue in the economics of a vegetable enterprise. In order to investigate the effect of biochar amendment and deficit irrigation on tomato fruit quality, experimental research was conducted under a rain shelter in southern China during the 2017 and 2018 growing seasons. The experiment consisted of five treatments. Crops were irrigated to 100% of field water capacity at all growth stages as treatments T1 and T2. The other treatments received 30% less irrigation water than T2 when its soil water content reached 70% of field capacity, and were designated as treatments T3, T4 and T5, applied at the vegetative (stage I), flowering and fruit development (stage II), and fruit ripening (stage III) stages, respectively. Treatment T1 included no biochar, while the other treatments included 10% biochar by weight. The results showed that the total soluble solids (TSS) content, sugar-to-acid ratio (SAR), vitamin C (VC) content, and colour index (CI) increased in the deficit irrigation treatments depending on the phenological stage, the fruit ripening stage in particular. Meanwhile, single fruit weight was significantly (p < 0.05) reduced by water deficit at stages II and III, subsequently affecting the total fruit yield. Biochar improved soil moisture conservation and had a positive effect on fruit quality as evidenced by better single quality attributes (p < 0.05) of T2 over T1. The GRA and TOPSIS appraisal methods were used to conduct the comprehensive quality analysis. Eventually, treatment T5 ranked the best in both seasons, and this was also confirmed by the combinational evaluation method.