The use of standard synthetic medications to treat inflammatory illnesses is associated with several negative effects. It has been shown that medicinal plants and their by-products are useful for safely treating inflammation. Herein, the essential oil of Eugenia supra-axillaris (family: Myrtaceae, ESA-EO) was isolated and further chemically characterized by GC-MS, and then, its nanoemulsion (ESA-EO-NE) was prepared. In addition, the anti-inflammation against the carrageenan-induced rats, the analgesic, and antipyretic activities of ESA-EO and ESA-EO-NE were evaluated in rats. Forty-three compounds were identified via GC-MS and categorized as mono- (61.38%) and sesquiterpenes (34.86%). d-limonene (32.82%), α-pinene (24.33%), germacrene-D (4.88%), α-humulene (4.73%), α-cadinol (3.39%), and trans-caryophyllene (3.15%) represented the main components. The administration of ES-EO and ES-EO-NE (50 and 100 mg/kg) demonstrated strong, dose-dependent inflammation inhibition capabilities in the model of rat paw edema, in comparison with both the reference drug and control. Reduced levels of malondialdehyde (MDA), increased levels of glutathione (GSH), and decreased levels of the proinflammatory cytokines (TNF-α), nitrosative (NO), and prostaglandin E2 (PGE2) in paw tissues all contributed to these substantial reductions in inflammation. Moreover, the oral administration of ESA-EO and ESA-EO-NE (50 and 100 mg/kg) exhibited potent analgesic and antipyretic activities in rats. Although the higher dose of ESA-EO and ESA-EO-NE (100 mg/kg) displayed delayed anti-inflammatory activity, they have long-lasting inflammation inhibition with fast onset and long-standing analgesic effects better than reference drugs. Furthermore, the most effective antipyretic efficacy was provided by ESA-EO-NE (100 mg/kg). These results provide insight into the possible therapeutic application of ESA-EO and its nanoemulsion against various inflammatory and painful illnesses as well as hyperthermia ailments.