Background: The number of breast cancer survivors is increasing, yet evidence to inform dietary and lifestyle guidelines is limited. Methods: This analysis included 3,658 participants from the Pathways Study, a prospective cohort of women diagnosed with invasive breast cancer. A healthy plant-based dietary index score (hPDI), an American Cancer Society nutrition guidelines score (ACS), a 2015 Healthy Eating Index score (HEI), hours per week of moderate to vigorous physical activity (PA) and lifetime cumulative pack-years of cigarette smoking (SM) were each measured at diagnosis, 6, 24 and 72 months. Using g-computation, 5- and 10-year risk ratios (RRs), risk differences (RDs), and 95% confidence intervals (CIs) for all-cause mortality under hypothetical interventions on diet quality, physical activity, and smoking, compared to the natural course (no intervention) were calculated. Results: Hypothetical moderate to extreme interventions on hPDI, ACS and HEI, each in combination with PA and SM, showed 11 to 56%, 9 to 38%, and 9 to 49% decreases in 5-year risks of all-cause mortality compared to no intervention, respectively [(hPDI: RRmoderate=0.89, 95% CI 0.82-0.94; RRextreme=0.44, 95% CI 0.26-0.67), (ACS: RRmoderate=0.91, 95% CI 0.85-0.96; RRextreme=0.62, 95% CI 0.43-0.82), (HEI: RRmoderate=0.91, 95% CI 0.84-0.95; RRextreme=0.51, 95% CI 0.33-0.72)]. While 10-year relative risks were slightly attenuated, absolute risk reductions were more pronounced. Conclusions: Interventions to improve diet quality, increase physical activity, or reduce smoking at the time of diagnosis may improve survival among breast cancer survivors. Impact: We estimate that over 10% of deaths could be delayed by even moderate adoption of these behaviors.