Background Increasingly, people who are not health professionals provide care for a partner, family member or friend affected by cancer, which can have negative effects on their health and well‐being. Psychosocial interventions that comprise psychological or social support and involve direct interaction between a healthcare professional and caregivers (or caregiver‐patient pairs) may help to address the negative health effects for caregivers. Review question What is the effectiveness of psychosocial interventions compared to usual care for informal caregivers of people living with cancer on a range of outcomes related to health and well‐being? Results We found19 trials that compared psychosocial interventions with usual care, in studies that included almost four thousand participants. Studies included caregivers of people affected by different cancers across all stages of the disease. There were differences in intervention make‐up. Intervention examples include providing information and/or teaching caregivers (or caregiver‐patient pairs) coping, communication or problem‐solving skills to manage symptoms or improve relationships. Interventions were delivered by nurses, psychologists or other professionals on an outpatient basis or at home via telephone. There may be a minimal benefit for caregiver quality‐of‐life immediately after the intervention, but this may not last. Psychosocial interventions may have little to no effect on quality of life for patients six to 12 months post‐intervention, but we are uncertain whether or not interventions improve quality of life for patients immediately post‐intervention. Psychosocial interventions may have little to no effect on caregiver depression, anxiety, distress and physical health and patient anxiety and distress at any time after the intervention, or on patient depression immediately and patient physical health six to 12 months post‐intervention. Psychosocial interventions probably have little to no effect on patient physical health immediately post‐intervention or patient depression three to six months post‐intervention. Three studies reported adverse effects including increased distress and sexual function‐related distress and lower relationship satisfaction levels for carers, increased distress levels for patients, and intervention content that was seen as inappropriate for some participants. No studies looked at cost‐effectiveness or intervention satisfaction for caregivers or patients. Because the quality of evidence was low generally, findings must be treated with caution. Conclusion Psychosocial interventions do not impact to a clinically meaningful degree outcomes for caregivers irrespective of patient cancer stage or type. Perhaps, other outcomes (e.g. relationship quality) or other psychosocial interventions (e.g. meditation) may be more helpful for caregivers. Interventions should be subjected to better conducted trials. Intervention development should involve caregivers and pay particular attention to individual personal needs.