Migration processes are often said to involve elements of choice and constraint in variable measure. However, this bipolar framing may fail to capture the twists and turns in many migrants’ erratic lives. In this article, we introduce the concept circumstantial migration to describe how migration trajectories and experiences unfold in unpredictable ways under the influence of micro-level context and coincidence. We expound on the concept through the case study of a cohort of Gambians who travelled to Guangzhou in South China, unexpectedly found that their prospects in China were limited, and struggled to leave the country. Our analysis examines the particularities of the Chinese immigration regime and its effects while presenting a broader argument against Chinese exceptionalism in migration studies. The concept of circumstantial migration underpins the questions guiding the analysis: how do latent influences trigger immediate circumstances? How do migrants engage with volatile circumstances? How are circumstances mediated by a variety of brokers? How does circumstantial migration produce particular temporalities? The core empirical data comes from interviews with returnees in Gambia, though the analysis draws upon extensive ethnographic fieldwork in Guangzhou over the past decade.