Objective: This systematic review and meta-analysis aimed to evaluate the effects of exercise interventions on cognitive function in diabetes. Methods: We conducted a comprehensive search of the Web of Science, PubMed, Scopus, EMBASE (Ovid), and SPORTDiscus databases from inception to December 2025 (registration number: CRD420251046731). The review included randomized controlled trials focusing on exercise interventions for diabetes and their impact on 4 cognitive domains: executive function, memory, attention, and global cognition. Subgroup and moderator analyses were performed based on exercise variables, including exercise type, session duration, total weekly exercise time, and intervention period. Study quality was assessed using the Cochrane Risk of Bias Tool 2 and the Physical Therapy Evidence Database scale (PEDro scale). Results: After screening 6230 records, 16 studies were included. Exercise interventions produced small-to-medium significant improvements in memory and global cognition in patients with diabetes, whereas the overall pooled effect on executive function was not statistically significant. Subgroup analyses suggested potential trends toward improvement in executive function for aerobic exercise (Hedge’s g = −0.30, p = 0.0039), single sessions ≥ 45 min (Hedge’s g = −0.40, p = 0.0463), and intervention periods ≥ 24 weeks (Hedge’s g = −0.27, p = 0.0383). For memory, aerobic (Hedge’s g = 0.27, p = 0.0131) or multicomponent exercise (Hedge’s g = 0.45, p = 0.0224) with single sessions ≤ 60 min (Hedge’s g = 0.28, p = 0.002), total weekly exercise time ≤ 120 min (Hedge’s g = 0.35, p = 0.0012), and interventions ≥ 12 weeks (Hedge’s g = 0.32, p = 0.0003) were significantly beneficial. Exercise also had a significant positive effect on global cognition (Hedge’s g = 0.49, p < 0.0001) without significant differences across exercise variables. In addition, exercise intervention showed a borderline, non-significant trend toward improved motor performance in patients with diabetes (Hedge’s g = 0.33, p = 0.0506). Conclusions: This comprehensive meta-analysis supports the beneficial effects of exercise on global cognition and memory in patients with diabetes. For memory enhancement, aerobic or multicomponent exercise protocols of ≥12 weeks, ≤120 min of total weekly exercise, and ≤60 min per session are more recommended. Although the overall pooled effect on executive function did not reach statistical significance, exploratory subgroup findings point toward potential domain-specific benefits under targeted exercise parameters (such as aerobic exercise of longer duration). These dose–response patterns should therefore be viewed as exploratory and hypothesis-generating, warranting confirmation in adequately powered, head-to-head trials before specific exercise prescriptions can be recommended.