The financial well-being of Emerging Adults (EAs) has long attracted scholarly attention, and the rapid expansion of OCC exposes them to structural risks that may ultimately undermine both their individual financial well-being and the stability of society. This study integrated financial literacy into the Theory of Planned Behaviour (TPB) framework to examine the mechanisms underlying Online Consumer Credit (OCC) adoption among Chinese EAs. Questionnaires were collected online through the Wenjuanxing platform, and 609 were valid. The findings revealed that attitudes, subjective norms, and perceived behavioural control positively influence EAs’ intention to use OCC, with intention serving as a key mediator between these antecedents and subsequent behaviours. Financial literacy moderated the intention–behaviour relationship, with higher levels of financial literacy weakening the link between people’s intention to adopt OCC and their actual usage. Moreover, subjective financial literacy exerted a stronger moderating effect than objective financial literacy. These results provide important implications for financial education initiatives. While objective knowledge is indispensable, confidence in one’s ability to make sound financial decisions may play a more decisive role in shaping life-long financial well-being. Future studies are recommended to explore additional moderators that may guide prudent OCC consumption and to localise research instruments for use in different cultural contexts.