<p>The purpose of the current study was to evaluate the effects of <i>Zataria multiflora</i> (<i>Z. multiflora</i>) and carvacrol supplementation on oxidative and antioxidant markers—including catalase, malondialdehyde (MDA), thiol, nitrite, and superoxide dismutase (SOD)—as well as inflammatory cell counts, through a systematic review and meta-analysis of randomized controlled trials. A literature search was conducted up to January 2025 using databases such as Web of Science, Scopus, PubMed/Medline, and Cochrane CENTRAL. This study evaluated the effects of oral supplements of <i>Zataria multiflora</i> and carvacrol on oxidant/antioxidant markers and inflammatory cell counts. A random-effects model was employed to synthesize standardized mean differences (SMD) and 95% confidence intervals (CI) for data analysis. Heterogeneity was assessed using the Cochrane Q test and I2 statistics. A total of nine studies were included in the meta-analysis, comprising 189 participants in the <i>Zataria multiflora</i> group and 111 in the control group. The levels of nitrite, MDA, total white blood cells (WBC), eosinophils, and monocytes were significantly decreased following the intake of <i>Z. multiflora</i> and carvacrol. Conversely, catalase activity, thiol levels, and lymphocyte counts showed a significant increase. The administration of <i>Z. multiflora</i> and carvacrol did not affect superoxide dismutase (SOD) activity or neutrophil counts. Subgroup analysis based on supplement type revealed a reduction in neutrophil counts with <i>Z. multiflora</i> intervention and an increase in SOD levels with carvacrol intervention. The findings of the current meta-analysis suggest that <i>Z. multiflora</i> and carvacrol may positively influence the regulation of the oxidant/antioxidant balance and reduce inflammatory cell activity.</p>