Few randomized controlled trials have examined the effects of combined aerobic and resistance training in breast cancer survivors soon after completing adjuvant therapy. Breast cancer survivors (N = 58) within 2 years of completing adjuvant therapy were randomly assigned to an immediate exercise group (IEG; n = 29) or a delayed exercise group (DEG; n = 29). The IEG completed 12 weeks of supervised aerobic and resistance exercise, three times per week. The DEG completed the program during the next 12 weeks. Participants completed patient-rated outcomes at baseline, 6, 12, 18 and 24 weeks. The primary endpoint was overall quality of life (QoL) measured by the Functional Assessment of Cancer Therapy-Breast scale. Secondary endpoints were fatigue, social physique anxiety, and physical fitness. Follow-up data was obtained on 97% of participants and exercise adherence was 61.3%. Repeated measures analyses of variance revealed a significant group by time interaction for overall QoL (P <0.001). Specifically, QoL increased in the IEG from baseline to 12 weeks by 20.8 points compared to a decrease in the DEG of 5.3 points (mean group difference = 26.1; 95% CI = 18.3-32.7; P <0.001). From 12 to 24 weeks, QoL increased in the DEG by 29.5 points compared to an increase of 6.5 points in the IEG (mean group difference = 23.0; 95% CI = 16.3-29.1; P <0.001). Similar results were obtained for the secondary endpoints. Combined aerobic and resistance exercise soon after the completion of breast cancer therapy produces large and rapid improvements in health-related outcomes.