Background: Asthma is a chronic inflammatory disease and a leading cause of disability, posing a huge economic and social burden. Plant-based antioxidants have the potential to block proinflammatory pathways and protect against oxidative damage, which could improve asthma management. Objective: This review examines the role of plant-based antioxidants as adjuvant therapy on inflammatory markers and clinical outcomes of adults with asthma. Methods: Digital databases, including Scopus, MEDLINE, EMBASE, CINAHL, PsycINFO, and Cochrane Airway Group's Specialized Register of Trials, were searched. Two independent authors performed initial and full-text screening of identified papers. The criteria for study inclusion and exclusion were predefined. Two authors independently performed data extraction and risk of bias as per the PRISMA checklist. Results: After full-text screening, nine randomized controlled trials were included in the final review. Seven of the included studies highlighted the efficacy of plant-based antioxidants in modulating the inflammatory cytokines in asthmatics. The benefits of antioxidants were also observed for improving oxidative status, lung functioning, and airway inflammatory markers. Furthermore, the overall quality of asthmatic patients’ lives was improved with fewer exacerbations such as night coughs and wheezing. Despite having some limitations, the overall risk of bias was low in this review. Conclusion: The review indicated that plant-based antioxidants could have adjuvant beneficial effects in the management of asthma inflammatory markers, which may help improve asthma-related clinical outcomes. However, due to the small number of study subjects, further research is required on the effect of plant-based antioxidants on asthma-inflammatory markers and clinical outcomes.