Increasingly health is recognised as a holistic construct that includes both mind and body. What is more, the bidirectional relationship between psychological wellbeing (PW) and physical health (PH) is becoming clearer. Psychological interventions have been shown to be effective at increasing PW and are widely accessible. However, there has not yet been a systematic synthesis of how improving PW using psychological interventions benefits PH. The aim of the study was to review the existing literature on how increasing PW via psychological interventions can improve PH, commenting on effectiveness and causal mechanisms, and suggesting directions for future research. A systematic review of peer reviewed studies was utilised. This took a broad search approach to include quantitative research concerning the impacts of psychological interventions on PH published between January 1998 and June 2022 in both clinical and non-clinical populations. From 1647 search results a total of 74 studies were included in the review with 10305 participants in total. Studies measured 139 individual PH outcomes for which 60 statistically significant effects were observed. Cognitive behavioural therapy-based interventions were most associated with both significant and non-significant effects, commonly impacting various self-report measures of PH. Positive psychology interventions (PPIs) also showed a higher proportion of significant effects. Mindfulness-based interventions had a clear link to reductions in cortisol, demonstrating significant effects in 2/3 studies. Pathways by which interventions improved PH broadly fell into three categories: 1) protect 2) reduce, and 3) produce. Within each category improvements were driven by biological, behavioural, or social support mechanisms. The present review supports the notion that psychological interventions can benefit PH and corroborates potential pathways that may drive this association. Future studies could benefit from defining PW better, thus unpacking the nuance in how targeting different areas of PW appears to impact different markers of PH.