Background There is great uncertainty regarding the practice of immediate autologous breast reconstruction (IBR) when post-mastectomy radiotherapy (PMRT) is indicated. Many plastic surgery units differ in their protocols, with some recommending delayed breast reconstruction (DBR) instead. Nevertheless, the cosmetic and psychosocial benefits offered by IBR are significant. The aim of this study was to comprehensively review and analyse existing literature to compare irradiated and unirradiated autologous flaps. Methods A comprehensive search in MEDLINE, EMBASE and CENTRAL databases was conducted in November 2020 for primary studies assessing outcomes of IBR with and without PMRT. Primary outcomes were the incidence of clinical complications, observer- and patient-reported outcomes. Meta-analyses were performed to obtain the pooled risk ratio of individual complications where possible. Results Twenty-one articles involving 3817 patients were included. Meta-analysis of pooled data demonstrated risk ratios for fat necrosis (RR=1.91, p<0.00001), secondary surgery (RR=1.62, p=0.03) and volume loss (RR=8.16, p<0.00001) favouring unirradiated flaps, but no significant difference in all other reported complications. The unirradiated group scored higher in observer-reported outcome measures, but self-reported aesthetic and general satisfaction rates were similar. Conclusions IBR should still be offered to patients as a viable option after mastectomy, even if they require PMRT. Despite the statistically significant higher risks of fat necrosis and contracture, these changes appear to be less clinically relevant, as corroborated by generally positive self-reported scores from patients who developed the aforementioned complications. Preoperative and intraoperative measures can further optimize reconstruction and mitigate post-radiation sequelae. Careful management of patients’ expectations is also imperative.