People in informal urban settlements in Kenya face multiple inequalities, yet researchers investigate issues such as HIV or intimate partner violence (IPV) in isolation, targeting single populations and focusing on individual behaviour, without involving informal settlement dwellers. We formed a study team of researchers (n = 4) and lay investigators (n = 11) from an informal settlement in Nairobi, Kenya to understand the power dynamics in the informal urban settlement that influence vulnerability to IPV and HIV among women and men from key populations in this context. We facilitated participatory workshops with 56 women and 32 men from different marginalised groups and interviewed 10 key informants. We used a participatory data analysis approach. Our findings suggest the IPV and HIV nexus is rooted in the daily struggle for cash and survival in the informal urban settlement where lucrative livelihoods are scarce and a few gatekeepers regulate access to opportunities. Power is gendered and used to exercise control over people and resources. Common coping strategies applied to mitigate against the effects of poverty and powerlessness amplify vulnerabilities to HIV and IPV. These complex power relations create and sustain an environment conducive to IPV and HIV. Prevention interventions thus need to address underlying structural drivers, uphold human rights, create safe environments, and promote participation to maximise and sustain the positive effects of biomedical, behavioural, and empowerment strategies.