Two field experiments were implemented to assess the possible protective role of chitosan against drought in sugar beet plants. Two carboxymethyl chitosan rates (0, tap water, and 200 mg L−1) were applied under three trickle irrigation levels of 60%, 80%, and 100% of the actual required water for the crop (W60, W80, and W100, respectively). Findings clarified that the maximum increase in catalase enzyme activity, flavonoids, and carotenoids was recorded under severe drought (W60) or moderate drought (W80) with chitosan supply. The chitosan-induced increase in the activity of glutathione peroxidase was more pronounced at the 60% level of watering. Chitosan increased the stomatal opening and pore area under different drought degrees. Owing to chitosan application, the increases in root yield reached 4.6 and 4.7% under well-watered (W100) and water deficit (W60), respectively. Chitosan application resulted in 4.9 and 9.2% increases in extracted sugar and sugar yield, respectively, under sufficient watering. Chitosan achieved substantial reductions in potassium and sodium under W60, which amounted to 2.6 and 8.0%, respectively. The increases in extracted sugar and sugar yield due to chitosan spraying were 5.3 and 10.7% with W60, as well as 7.4 and 12.1% with W100, respectively. Furthermore, chitosan improved water use efficiency by 9.6% compared to the control (plants untreated with chitosan). In conclusion, under normal or deficit water irrigation conditions, treating the sugar beet crop with 200 mg L−1 of carboxymethyl chitosan is recommended to ensure better sugar yield and sugary juice quality while improving water use efficiency.