Objectives: To determine the effects of the 3-month multicomponent Better Exercise Adherence after Treatment for Cancer (BEAT Cancer) physical activity behavior change intervention on fatigue, depressive symptomatology, and anxiety. Methods: Postprimary treatment breast cancer survivors (n = 222) were randomized to BEAT Cancer or usual care. Fatigue Symptom Inventory and Hospital Anxiety and Depression Scale were assessed at baseline, postintervention (month 3; M3), and follow-up (month 6; M6). Results: Adjusted linear mixed-model analyses demonstrated significant effects of BEAT Cancer vs usual care on fatigue intensity (M3 mean between group difference [M] = −0.6; 95% confidence interval [CI] = −1.0 to −0.2; effect size [d] = −0.32; P =.004), fatigue interference (M3 M = −0.8; CI = −1.3 to −0.4; d = −0.40; P <.001), depressive symptomatology (M3 M = −1.3; CI = −2.0 to −0.6; d = −0.38; P <.001), and anxiety (M3 M = −1.3; CI = −2.0 to −0.5; d = −0.33; P <.001). BEAT Cancer effects remained significant at M6 for all outcomes (all P values <.05; d = −0.21 to −.35). Clinically meaningful effects were noted for fatigue intensity, fatigue interference, and depressive symptomatology. Conclusions: BEAT Cancer reduces fatigue, depressive symptomatology, and anxiety up to 3 months postintervention in postprimary treatment breast cancer survivors. Further study is needed to determine sustainable methods for disseminating and implementing the beneficial intervention components.