A key driver of obesity and diet-related illness globally has been the increased consumption of ultra-processed foods (UPFs). This paper aimed to identify the key actors, structures, incentives, and dynamics that characterize the global UPF system and have led to the dominance of UPFs in population diets. Based on a narrative review and using a systems thinking approach, we developed a causal loop diagram (CLD) of the global UPF system. The CLD comprises nine reinforcing loops: the commodification of diets; increasing market concentration; increasing UPF levels in food retail environments; the financialization of diets; direct corporate political influence; increasing capture of science, public opinion, and policy narratives; shifts from private to public food governance; state accommodation of corporate power; and an "agricultural regime" promoting the production of relatively cheap UPF inputs. The CLD also contains two balancing loops relating to market saturation and public health policies that curb UPF consumption and a countervailing reinforcing loop depicting other forms of food systems in tension with the UPF system. This study suggests the need for innovative and expansive government policies to protect and promote healthy, sustainable diets and coordinated advocacy efforts among those seeking to challenge the exploitative aspects of corporate food systems.