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.