Purpose The purpose of the study is to systematically review and synthesise randomised controlled trials investigating the effectiveness of prehabilitation compared to usual care for newly diagnosed, adult-onset cancer patients. Methods MEDLINE, EMBASE, PsycINFO, CINAHL and SSCI were searched up to April 2017. Studies were included if disease-related, treatment-related, patient-reported and health service utilisation outcomes were assessed. Two reviewers independently reviewed and appraised the risk of bias of each study. Results Eighteen studies were included. Interventions comprised one or more of the following components: psychological support, education and exercise. Meta-analyses found that pelvic floor muscle training (PFMT) significantly increased odds of continence at 3 months (OR = 3.29, 95% CI = 1.57-6.91), but did not significantly reduce daily pad use at 6 months post-surgery Mean Difference (MD)= ( = − 0.96, 95% CI = − 2.04-0.12) for prostate cancer patients. Although quality of life improved due to PFMT, functional ability or distress did not. Further meta-analyses indicated that presurgical exercise significantly reduced length of hospital stay (MD = − 4.18, 95% CI = − 5.43-− 2.93) and significantly lowered odds of post-surgery complications (OR = 0.25, 95% CI = 0.10-0.66) for lung cancer patients. Psychology-based prehabilitation significantly improved mood, physical wellbeing and immune function for prostate cancer patients and improved fatigue and psychological outcomes and a trend for better quality of life among breast cancer patients. Risk of bias was high for most studies. Conclusions Prehabilitation appears to benefit cancer patients. Rigorous trials are needed to investigate the effectiveness of prehabilitation among other cancer sites and other related effects. The cost-effectiveness of prehabilitation remains unanswered. Implications for cancer survivors Providing interventions earlier in the care pathway may lead to better outcomes for patients during survivorship.