This study investigates the effects of polyvinyl chloride (PVC) microplastics (MPs) and chromium (Cr) on the growth, photosynthesis, respiration, electrolyte leakage, oxidative stress, and gas exchange attributes of *Trachyspermum ammi* (ajwain) seedlings, along with the protective role of titanium dioxide (TiO₂) nanoparticles (NPs). The results show that increasing levels of Cr and PVC-MPs significantly reduce plant growth, biomass, photosynthetic pigments, gas exchange parameters, sugars, and nutritional content. Conversely, these stressors increase oxidative stress indicators such as malondialdehyde, hydrogen peroxide, and electrolyte leakage, and organic acid exudation in the roots of *T. ammi* seedlings. However, the application of TiO₂-NPs counteracts the toxicity of Cr and PVC-MPs, leading to improved plant growth and biomass. This protective effect is attributed to the ability of NPs to sequester reactive oxygen species, reducing oxidative stress and lowering Cr concentrations in both the roots and shoots of the plants. The study highlights the potential of TiO₂-NPs in enhancing the resilience of *T. ammi* seedlings to Cr and PVC-MPs toxicity, resulting in improved biomass and healthier physiological states.This study investigates the effects of polyvinyl chloride (PVC) microplastics (MPs) and chromium (Cr) on the growth, photosynthesis, respiration, electrolyte leakage, oxidative stress, and gas exchange attributes of *Trachyspermum ammi* (ajwain) seedlings, along with the protective role of titanium dioxide (TiO₂) nanoparticles (NPs). The results show that increasing levels of Cr and PVC-MPs significantly reduce plant growth, biomass, photosynthetic pigments, gas exchange parameters, sugars, and nutritional content. Conversely, these stressors increase oxidative stress indicators such as malondialdehyde, hydrogen peroxide, and electrolyte leakage, and organic acid exudation in the roots of *T. ammi* seedlings. However, the application of TiO₂-NPs counteracts the toxicity of Cr and PVC-MPs, leading to improved plant growth and biomass. This protective effect is attributed to the ability of NPs to sequester reactive oxygen species, reducing oxidative stress and lowering Cr concentrations in both the roots and shoots of the plants. The study highlights the potential of TiO₂-NPs in enhancing the resilience of *T. ammi* seedlings to Cr and PVC-MPs toxicity, resulting in improved biomass and healthier physiological states.