Refugees encounter multiple psychosocial stressors post-resettlement which increases their risk of developing a mental illness. Loneliness and social isolation are commonly reported in the refugee population and have been demonstrated to be associated with multiple physical and mental health comorbidities in the general population. However, no study to date has systematically reviewed how loneliness and social isolation may affect refugees who have resettled in high-income countries. This systematic review aims to study the prevalence, risk factors, consequences, and interventions for loneliness and social isolation among refugees who have resettled in high-income countries. Systematic searches on five electronic databases yielded 2950 papers, of which 69 were deemed eligible following a double-blinded review by title and abstract then later by full text. From the included studies, it was found that the reported range of prevalence rates of loneliness (15.9-47.7%) and social isolation (9.8-61.2%) were higher than population norms. Risk factors associated with loneliness and social isolation included family separation, acculturative stress, being female or a parent and a current diagnosis of a mental illness. Loneliness and social isolation were found to be associated with depression, post-traumatic stress disorder (PTSD), psychological distress as well as physical health problems. Only three interventions addressing loneliness and social isolation were identified which demonstrates the importance of integrating social support in refugee psycho-social support programs. In summary, loneliness and social isolation were reported by a large proportion of refugees who have resettled in high-income countries. Whilst certain risk factors were pre-migratory and static, most were post-migratory in nature and were found to adversely affect mental and physical health. Thus, interventions focused on reducing loneliness and social isolation that are guided by the needs of refugee communities are urgently required.