HIV infection and intimate partner violence (IPV) share a common risk environment in much of southern Africa. We implemented a structural intervention that combined a microfinance programme with a gender and HIV training curriculum and assessed changes in economic well-being, gender equity, social capital and vulnerability to HIV and IPV. Eight villages were pair-matched and randomly allocated to receive the intervention at study onset or three years later. Loans were provided to poor women enrolling in the intervention. A participatory learning and action curriculum was integrated into fortnightly loan meetings. Effect estimates were generated for outcome measures among direct programme participants (Cohort 1) and 14-35 year old household (Cohort 2) and community members (Cohort 3), alongside matched controls. Among direct programme recipients, effect estimates suggested improvements in economic well-being, social capital, and empowerment relative to matched controls. Within this cohort, 12 month experience of physical and/or sexual abuse was reduced by 55% (aRR 0·45 95% CI 0·23-0·91). No data on HIV risk were collected from this cohort. Modest effects on vulnerability to HIV were seen among indirect programme recipients. Among Cohort 2 (14-35 year old household members) greater levels of openness and communication about sex/sexuality were reported. No behavioural effects were observed (aRR for unprotected intercourse at last sex with a non-spousal partner 1·02 95% CI 0·85-1·23). Among Cohort 3 (14-35 year old community members) there was a suggestion that partner numbers were reduced (aRR for more than one partner in the last year 0·64 95% CI 0·19-2·16) but there was no effect on the rate of unprotected intercourse at last sex with a non-spousal partner (aRR 0·89 95% CI 0·66-1·19) or HIV incidence (aRR 1·06 95% CI 0·66-1·69). The study provides evidence that a combined microfinance and training intervention has the potential to generate social and economic benefits, and lead to reductions in levels of IPV among programme participants. There was very limited evidence of wider indirect effects on HIV risk among young people in the short term. Social and economic development interventions have the potential to alter risk environments for HIV and IPV in southern Africa and should be evaluated further.