In this study, we investigated the volatile composition of the Algerian medicinal plant Calendula arvensis, as well as the antioxidant evaluation, total phenolics and flavonoids contents, and synergistic antibacterial effect of its ethanolic extract (CAEE) with chemical antibiotics against some bacterial strains. The results of the GC-MS and GC-FID analyses revealed the existence of 67 compounds, with the major constituents being δ-cadinene (11.6%), α-muurolol (9.3%), cubeban-11-ol (9.1%), α-cadinol (8.4%), epi-α bisabolol (7.5%), phytol (7.3%), epi-cubebol (4.0%), α-bisabolol (3.9%), and neophytadiene (3.8%). Certain volatile components, including neophytadiene, geijerene, α-terpineol, cogeijerene, γ himachalene, 5-hydroxycalamenene, methyl docosanoate, heptacosane, methyle tetracosanoate, nonacosane, uncontane, and muurol-5-en-4-α-ol skeletons, were detected for the first time in C. arvensis oil. In addition, a remarkable synergistic effect was reported for CAEE against E. coli, resulting in the re-sensitization of the E. coli-resistant strain to penicillin. Indeed, phenols and flavonoids were also presented in CAEE with moderate concentrations (17.7 µg GAE/mg and 12.9 µg QE/mg, respectively) and correlated positively with its moderate antioxidant capacity. These findings imply that this species might be a valuable source of antibacterial and antioxidant chemicals in the future.