Randomized control trials exploring adjuvant supportive-expressive group therapy (SEGT) for breast cancer have yielded conflicting survival results. This retrospective cohort study was designed to explore the association of adjuvant SEGT performed at diagnosis with survival in real-world patients. 3327 patients with breast cancer were divided between those who received oncologic treatment combined with SEGT-based intervention (referred to as BRBC [n = 354]) and those who only received oncologic treatment (referred to as OT [n = 2973]). Primary outcome was overall survival (OS) at 1-year, 3-year, 5-year. Propensity score-matched analysis (at a ratio of 1:3) and instrumental variable analysis (IVA) were performed. The median overall survival was 7.3 years (95% CI 7.0-7.7 years) in BRBC and 7.1 years (95% CI 6.9-7.4 years) in OT. BRBC was not significantly associated with improved 1-year (HR 0.74, 95% CI 0.49-1.10, P = 0.1748; NNT = 44.8, 95% CI - 118.5 to 22.6), 3-year (HR 0.98, 95% CI 0.75-1.27, P = 0.8640; NNT = 273.7, 95% CI - 21.0 to 21.3), or 5-year survival (HR 0.79, 95% CI 0.61-1.02, P = 0.0908; NNT = 36.0, 95% CI - 384.5 to 19.1) compared with OT. IVA indicated that BRBC had a survival benefit over OT in the 1-year, 3-year, and 5-year of 1.5% (95% CI 1.2-1.9%), 0.7% (95% CI 0.6-0.8%), and 2.6% (95% CI 2.0-3.4%), respectively. Adjuvant SEGT cannot significantly prolong 5-year survival in breast cancer, though a longer observation period is warranted according to the marginal survival benefit identified at the end of the follow-up.