Background: Overwhelming randomized controlled trial evidence demonstrates that exercise has positive health impacts during and after treatment for breast cancer. Yet, evidence generated by studies in which exercise programs are delivered outside a tightly controlled randomized trial setting is limited. The purpose of this study was to assess the effectiveness of an evidence-based exercise program with real-world implementation on physical fitness and quality of life (QoL). Patients and Methods: Oncologists referred women with early-stage breast cancer who were scheduled to receive adjuvant chemotherapy. The program consisted of supervised aerobic and resistance exercise of moderate to vigorous intensity 3 times per week until the end of treatment (chemotherapy ± radiotherapy), then twice per week for 10 weeks, followed by once per week for 10 weeks. Health-related physical fitness and QoL were assessed at baseline, end of treatment, end of program, and 1-year follow-up. Results: A total of 73 women were enrolled. Estimated peak VO2 (VO2peak), QoL, and body weight were maintained between baseline and end of treatment, whereas muscular strength improved (P<.01). By the end of the program, VO2peak, heart rate recovery, waist circumference, and some aspects of QoL were improved (all P<.01) relative to baseline. One year later, VO2peak, QoL, and waist circumference were maintained relative to end of program, whereas the improvements in strength and heart rate recovery had dissipated (all P<.01). Conclusions: Evidence-based exercise programming delivered with real-world implementation maintained VO2peak, strength, and QoL during adjuvant treatment and improved these measures after treatment completion among women with breast cancer. Continued guidance and support may be required for long-term maintenance of strength improvements in this population.