Background Patients with diabetes mellitus (DM) often experience psychological challenges, such as feelings of loss of control, self-care stress, and fear of complications. This study aimed to assess the prevalence of uncontrolled DM, self-efficacy, quality of life (QoL), and well-being among patients with DM in Alqunfudah, Saudi Arabia, and to investigate the associations between these factors and diabetes control. Methods A cross-sectional study employing an online questionnaire was conducted among adults with DM. The questionnaire assessed demographic characteristics, diabetes-related history, and glycemic control based on glycated hemoglobin A1c (HbA1c) level. Self-efficacy was evaluated using the validated Arabic version of the Self-Efficacy for Managing Chronic Disease 6-Item Scale, and the Arabic version of the World Health Organization Quality of Life Brief Version was utilized to assess QoL. Well-being was measured using the Arabic version of the World Health Organization-Five Well-being Index (WHO-5). Results Four hundred patients with diabetes were included with a mean age of 49.3 +/- 14.6 years, 40.8% were males, and 49.25% had uncontrolled DM. Compared to the controlled group, the uncontrolled group had a lower percentage of patients living in urban areas (16.8% vs. 25.6%, p = 0.037), a larger proportion of participants having DM for > 10 years (42.6% vs. 26.6%, p < 0.001), lower median (interquartile [IQR]) self-efficacy score [39.0 (30.0-46.0) vs. 47.0 (34.0-54.0), p < 0.001], lower physical QoL [75.0(60.7-85.7) vs. 67.8 (50.0-82.1), p < 0.001], and lower environmental QoL [(78.1(62.5-87.5) vs. 68.7(59.3-84.3), p = 0.005]. Predictors of glycemic control included the physical domain of QoL [adjusted odd ratio (aOR) = 1.02 (95% CI: 1.01-1.03), p < 0.001] duration of DM for 1-2 years [aOR = 2.53 (95% CI: 1.08-5.91), p= 0.032], 3-5 years [aOR = 3.76 (95% CI: 1.90-7.43), p< 0.001 ], and 6-10 years [aOR = 1.85 (95% CI: 1.04-3.32), p = 0.036], and urban residence [aOR = 1.88 (95% CI: 1.11-3.18), p = 0.017]. Conclusions A large sector of patients with diabetes had uncontrolled blood sugar with greater affection of QoL and self-efficacy compared to the controlled group. Physical QoL, duration of DM, and residence were the key factors to be targeted for improved diabetes management.