Poor glycemic control remains a pervasive challenge in type 2 diabetes mellitus (T2DM) management, contributing to elevated risks of complications and healthcare burdens globally. This systematic review aimed to synthesize evidence on the determinants of poor glycemic control (hemoglobin A1C (HbA1c) >
7%) among adults with T2DM. We followed PRISMA guidelines to search for relevant studies across five different databases, where we found 239 studies. First, the studies were screened for duplicates and then assessed for eligibility by screening through titles, abstracts, and ultimately full text. Upon carefully assessing for eligibility using inclusion and exclusion criteria, only 12 studies were found relevant and were included in this systematic review. The review found that most studies had a moderate risk of bias based on the Newcastle-Ottawa Scale, with only three rated as low risk. Key factors linked to poor glycemic control included low socioeconomic status, medication non-adherence, longer diabetes duration, obesity, insulin-based regimens, and limited access to healthcare. Insulin use, in particular, was paradoxically associated with worse control due to its complexity and adherence challenges, especially in low-resource settings. Regional differences highlighted unique barriers like cultural practices in Ethiopia and gaps in diabetes education in Eritrea. These findings reflect the complex and context-specific nature of glycemic control, especially in low- and middle-income countries. The review calls for simplified treatments, affordable medications, and better management of comorbidities, while encouraging future research using longitudinal and mixed-methods approaches to guide more effective, patient-centered interventions.