Diabetes mellitus (DM) is assuming epidemic proportions worldwide, particularly in developing countries. Identifying the current burden of DM in Nigeria is essential for effective healthcare planning and resource allocation for prevention. This review aimed to determine the current prevalence and risk factors of DM across the six geopolitical zones of Nigeria over the last two decades. Using the preferred reporting items for systematic review and meta-analysis (PRISMA) study design, articles pertinent to the study objective were searched from 2000 to 2024. The quality of the studies included in this review was assessed using the Joanna Briggs Institute (JBI) critical appraisal tool for descriptive studies. Forty-four full-text publications met the eligibility criteria, out of which 23 were excluded because only an abstract was published, and 21 articles were included in the review. The overall pooled prevalence of DM in Nigeria was 6.3%. The prevalence of DM in the six geopolitical zones of Nigeria was 6.2% in the north-west, 6.1% in the north-east, 5.6% in the north-central zone, 5.4% in the south-west, 13.1% in the south-east, and 6.0% in the south-south zone. The prevalence of DM in Nigeria has increased over the last two decades compared to previous reports. Physical inactivity, unhealthy diet, and obesity are important perpetuating factors. A national diabetes care and prevention policy is highly recommended.