BACKGROUND: The COVID-19 pandemic has posed significant challenges to global health, with type 2 diabetes mellitus (T2DM) emerging as a key risk factor for adverse outcomes. This study systematically reviews and quantifies the association between T2DM and COVID-19 outcomes, including mortality, severity, and need for mechanical ventilation. METHODS: A systematic review and meta-analysis were conducted that adhered to PRISMA guidelines. We searched PubMed, Scopus, Web of Science and Embase for studies published from december 2019 to march 2024. Eligible studies reported on the impact of T2DM on COVID-19 outcomes in the adult population. Data were extracted and analyzed using a random-effects model, and heterogeneity was assessed using the I statistic. Publication bias was assessed using Egger regression, Kendall's Tau, and the Fail-safe N calculation. RESULTS: Eighteen studies were included in the meta-analysis for mortality, six for severity and five for mechanical ventilation. T2DM was significantly associated with higher mortality (OR = 3.66, 95% CI: 2.20-5.11, p < 0.001), higher severity (OR = 1.97, 95% CI: 1.02-2.92, p < 0.001), and higher need for mechanical ventilation (OR = 2.34, 95% CI: 1.18-3.49, p < 0.001). Heterogeneity was high for mortality (I = 83.83%) but low for severity and mechanical ventilation (I = 0%). No significant publication bias was found. CONCLUSIONS: T2DM is associated with significantly worse outcomes in COVID-19 patients, including higher mortality, higher severity and a greater likelihood of needing mechanical ventilation. These findings emphasize the need for targeted interventions and management strategies for individuals with T2DM during the ongoing pandemic. Future research should focus on understanding the underlying mechanisms and exploring strategies to mitigate these risks.