Energy poverty—difficulty achieving adequate indoor thermal comfort—has been consistently linked to poorer mental health. Yet the effects of corrective interventions on validated mental-health outcomes remain unclearQuantify the impact of interventions that reduce energy poverty (fabric insulation, draught-proofing, central-heating, whole-house packages, and educational advice) on validated mental-health outcomes versus usual care/no intervention or alternative interventions.We registered a protocol (PRISMA 2020) and searched MEDLINE/PubMed, Embase, Scopus, Web of Science, CENTRAL, PsycINFO, CINAHL and grey sources (2005–2025). Eligible studies evaluated interventions targeting thermal comfort/affordability (fabric insulation, heating systems, whole-house retrofits, behavioural advice) and reported validated mental-health outcomes (e.g., GHQ-12, SF-12/36 MCS, HADS/PHQ/GAD). We included randomised and non-randomised comparative designs and undertook random-effects meta-analyses by intervention class where ≥3 comparable estimates were available; otherwise, we applied SWiM narrative synthesis. Risk of bias was assessed with RoB 2/ROBINS-I; certainty with GRADE.Eight intervention studies met criteria (United Kingdom n=6, New Zealand n=1, Portugal n=1), including one cluster RCT and seven non-randomised evaluations. Structural fabric upgrades and heating/system improvements were most common; purely behavioural/educational interventions were rare. Pooled effects (GHQ-12/SF-12 MCS) suggested small but clinically meaningful improvements in psychological distress/mental health following fabric upgrades and combined packages; system-only upgrades showed modest, directionally similar gains. Heterogeneity was moderate, reflecting differences in intervention bundles, populations and instruments. Subgroup evidence—limited but consistent—indicated larger benefits among more deprived households and those with poorer baseline thermal performance. Cost-effectiveness analyses (mainly UK) favoured insulation/heating upgrades when mental-health gains and co-benefits were included. Overall risk of bias was “some concerns” (cRCT) and “moderate–serious” (non-randomised) due to confounding, selection and self-report; GRADE certainty was low to moderate.Energy-efficiency retrofits—especially insulation combined with controllable heating—yield modest, consistent improvements in GHQ-12 and MCS, likely mediated by thermal comfort and reduced bill stress. Benefits appear larger in the coldest, most deprived homes. Evidence remains constrained by bias and heterogeneity; stronger, longer studies with objective mediators and economic evaluation are priorities.Energy-efficiency retrofits—especially insulation and central-heating packages—likely improve mental-health outcomes, with equity-relevant gains in high-need groups. Stronger evidence is needed from well-designed RCTs/quasi-experiments using standardised mental-health measures, longer follow-up and cost-utility endpoints, particularly beyond the UK.