Purpose The incidence of the breast cancer has increased globally in recent years. In patients with large primary breast cancer and/or with positive lymph nodes, post-mastectomy radiotherapy (PMRT) is proven to decrease the chances of locoregional recurrence and lower mortality rates. In the setting of immediate implant-based breast reconstruction however, data on long term outcomes is limited. This study aimed to uncover then long-term surgical and oncological outcomes of patients who underwent PMRT with implant based breast reconstruction. Methodology This is a retrospective cohort study of data collected from two Australian oncoplastic breast surgeons. Subjects were women who had a mastectomy and received PMRT for various breast cancer types over a 5-year period. Demographic data, cancer characteristics and post-operative outcomes were collected. Statistical analysis was performed on Prism GraphPad using 95% confidence intervals. Results A total of 135 women were included. Average age and BMI was 48 years old and 24.23 (95% CI 23-25) respectively. Long term complications were reported in 45% of females, and included capsular contraction (19%), breast asymmetry (6%), implant malposition (4%), secondary infection (3%), implant rippling (2%), nipple displacement (1%), implant loss (<1%). At a median follow up time of 27 months (95% CI 23-30), 36% required revisional surgery. Cancer recurrence affected only 4 women (n=1 local, n=3 distant). Conclusion Breast reconstruction with implants followed by PMRT, although is associate with lower recurrence and mortality rates, does carry a higher complication profile.