Physical inactivity is highly common in adults with type 1 diabetes (T1D) as specific barriers (i.e., hypoglycemia) may prevent them from being active. The objective of this study was to examine the efficacy of the Physical Exercise Promotion program in type 1 diabetes (PEP-1) program, a group program of physical activity (PA) promotion (intervention) compared with an information leaflet (control), to improve total energy expenditure (TEE) in adults with T1D after 12 weeks. TEE was measured with a motion sensor over a 7-day period at inclusion, after the program (12 weeks) and 1-year after inclusion. The 12 weekly sessions of the program included a 30-min information session (glycemic control and PA) and 60 min of PA. A total of 48 adults, aged 18 to 65 years with a reported PA practice <150 min per week, were recruited (45.8% men; aged 44.6 ± 13.3 years; 8.0% ± 1.1% glycated hemoglobin (A1c)) and randomized in this pilot trial. Ninety percent of participants completed the program and 88% completed the 1-year follow-up. No change was observed for TEE and A1c in both groups. After the 12-week program, the mean peak oxygen uptake increased (14%; p = 0.003) in the intervention group; however, at the 1-year follow-up, it was no longer different from baseline. In the control group, no difference was observed for the peak oxygen uptake. These results suggest that the PEP-1 pilot program could increase cardiorespiratory fitness. However, this benefit is not sustained over a long-term period. The PEP-1 program did not increase TEE in patients with T1D and other strategies remain necessary to counteract physical inactivity in this population.