Cinnamomum cassia (C. assia) has long been used in traditional holistic medicine for its medicinal properties. It is used as an antioxidant, antibacterial, anti-inflammatory and anticancer agent. Cinnamon, in particular, the essential oil of C. cassia, has significant biological properties. Despite this, the volatility, stability, and insolubility of C. cassia essential oil (CEO) remain the main disadvantages that limit its application, ultimately affecting its pharmacological efficacy. To find a solution to this problem, we developed the CEO nanoemulsion (CEO-NE). For lipophilic compounds, insoluble nanoemulsion-based formulations are a popular delivery strategy. In this research work, a highly stable dosage form named CEO-NE was successfully developed using polysorbate 80 and water. The findings show that the synthesized CEO has a uniform shape with a PDI of 0.380 and an adequate particle size of 221.8 nm. The antioxidant outcomes show excellent results for CEO-NE compared to CEO against DPPH and hydrogen peroxide. The obtained antibacterial activity of CEO-NE was more efficient than that of CEO against Klebsiella pneumonia (MTCC 8911) with 0.025% and 0.05%, respectively. The CEO-NE preparation was tested against an alveolar lung adenocarcinoma cell line (A549) with an IC50 of 50.21 µg/mL for CEO and 18.05 µg/mL for CEO-NE, respectively. These results are encouraging for future translational studies on CEO-NE use in lung cancer therapy due to its excellent antioxidant, antibacterial, and killing kinetic properties.