Background: Physical activity is an important predictor of quality of life in older adults with type 2 diabetes (T2D). Unfortunately, most T2D adults adopt a sedentary lifestyle. The randomized, controlled TRIPL-A trial aims to verify the effect of a personalized, discontinuous exercise program on a sedentary lifestyle of T2D older adults. Methods: A total of 305 T2D patients (mean age ± SD: 68.8 ± 3.3 years) were divided into a control arm receiving only behavioral counseling and an intervention arm of an 18-month supervised discontinuous exercise program (ERS). The primary outcomes were the changes in sitting time (ST) and metabolic equivalent (MET) values, both evaluated by the International Physical Activity Questionnaire short form. A repeated measures ANOVA with Bonferroni correction for multiple comparisons was used to compare study outcomes. Results: The ST and MET differed significantly during the study compared to the control group (p = 0.028 and p = 0.004, respectively). In the intervention group, a decrease from baseline in ST at 6 months (p = 0.01) and an increase in MET values at 6 months (p = 0.01) up to 12 months (p < 0.01) were found. No significant differences were found for the other variables. Conclusions: Beneficial lifestyle changes were found within the first year of intervention. These results align with the theory of change.