Over the past few decades, the financial sector has sought to positively contributing to sustainable development through innovative products and services. However, in its business-as-usual the financial sector continues to contribute to military interventions, environmental degradation, growing disparity of incomes, de-coupling of finance and real economy, and global economic crises. This article presents a framework of how to appraise the positive and negative contributions of the financial sector to sustainable development, from a systems perspective. On this base, the article proposes an approach for designing effective finance interventions to complex sustainability problems. Based on similar experiences from studies on water governance and technology development, the approach proposes a participatory procedure, first, to identify the role of the financial sector in complex sustainability problem constellations and, second, to develop intervention strategies for financial intermediaries interested in shifting their role and mitigating the identified problems. We discuss challenges of establishing causal links within the problem constellation, which is a prerequisite for successful intervention design, as well as in the cause–effect structure of the interventions themselves. The article concludes with outlining future research needs.