BackgroundPeople with mental health difficulties often experience social isolation. The importance of interventions to enhance social networks and reduce this isolation is increasingly being recognised. However, the literature has not yet been systematically reviewed with regards to how these are best used. This narrative synthesis aimed to investigate the role of social network interventions for people with mental health difficulties and identify barriers and facilitators to effective delivery. This was undertaken with a view to understanding how social network interventions might work best in the mental health field.MethodsSystematic searches using combinations of synonyms for mental health difficulties and social network interventions were undertaken across 7 databases (MEDLINE, Embase, PsycINFO, CINAHL, Cochrane Library, Web of Science) and 2 grey literature databases (EThoS and OpenGrey) from their inception to October 2021. We included studies reporting primary qualitative and quantitative data from all study types relating to the use of social network interventions for people with mental health difficulties. The quality of included studies was assessed using the Mixed Methods Appraisal Tool. Data were extracted and synthesised narratively.ResultsThe review included 54 studies, reporting data from 6,249 participants. Social network interventions were generally beneficial for people with mental health difficulties but heterogeneity in intervention type, implementation and evaluation made it difficult to draw definitive conclusions. Interventions worked best when they (1) were personalised to individual needs, interests and health, (2) were delivered outside formal health services and (3) provided the opportunity to engage in authentic valued activities. Several barriers to access were identified which, without careful consideration could exacerbate existing health inequalities. Further research is required to fully understand condition-specific barriers which may limit access to, and efficacy of, interventions.ConclusionsStrategies for improving social networks for people with mental health difficulties should focus on supporting engagement with personalised and supported social activities outside of formal mental health services. To optimise access and uptake, accessibility barriers should be carefully considered within implementation contexts and equality, diversity and inclusion should be prioritised in intervention design, delivery and evaluation and in future research.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12888-023-04881-y.