Over the past thirty years, a growing number of countries with diverse state-economy relations have established Sovereign Wealth Funds (SWFs), which are fully state-owned investment vehicles that allocate public capital in financial markets through commercially oriented, profit-driven strategies. The global rise of SWFs reflects a central tension in the revival of state-led finance in the twenty-first century. These funds can serve as politicised tools of state investment or as mechanisms that advance the marketisation of public financial management. To improve our understanding of SWFs as both investors, agents of the state, and, therein their role in reshaping state-market relationships, this thesis investigates two core questions: What explains the growing creation of SWFs since the 1990s? And how do states choose to structure their relationship with SWF managers? I argue that the trend toward SWF creation was triggered by the Asian Financial Crisis of 1997 and the Global Financial Crisis of 2008–09. Faced with pressure to respond to these shocks while protecting financial interests, governments created SWFs as market-oriented instruments of state-led finance that could address rising economic challenges in ways which support and draw on financial markets rather than impede them. However, countries organise the governance arrangements of these funds in ways that reflect prevailing models of state-market interaction. Where state involvement in the economy is more accepted, SWFs thereby may become instruments of politicised public investment. In contexts where the state acts primarily as a regulator and promoter of markets, SWFs are more likely to reinforce market-oriented approaches by delegating the allocation of public capital to financial experts and market logics. The thesis supports these claims through a mixed-methods design, combining cross-national data on SWF creation between 1970 and 2018, a novel dataset on the governance structures of 60 SWFs in 2022, and four case studies of Ireland, France, Nigeria, and China. The findings show that the Global Financial Crisis in particular spurred new SWF creation as a state-led, market-oriented response to rising economic challenges. They also demonstrate that governance structures reflect nationally specific ideas about how the state should engage with the economy. In doing so, the thesis sheds light on both the causes behind the global proliferation of SWFs and the variation in how they operate as agents of the state. It identifies the conditions under which SWFs are likely to become politicised instruments of state-led investment, as opposed to vehicles for the marketisation of public finance. This contributes to three key strands of scholarship: the literature on the revitalisation of state-led finance in the twenty-first century, the study of how economic crises shape policy trajectories, and the comparative capitalism literature concerned with the persistence of divergent approaches to state-economy relations.