Previous research has shown that motivation, epistemic beliefs, and perceived social support each have an effect on the way students engage in their learning and can promote a deep approach. The first aim of this study was to measure and compare these effects. Some authors have argued that epistemic beliefs and perceived social support do not have a direct effect on approach to learning, but that this effect is mediated by motivation. The second aim of this study was to examine this hypothesis and, more specifically, to determine the extent to which the effects of evaluativist epistemic beliefs and perceived social support promote a deep approach to learning directly or indirectly through self-determined and controlled motivation. We adopted a cross-sectional study design and focused on the first year of university. This study is based on the responses of 2168 French first year university students to a questionnaire. Linear regression shows that the strongest factor predicting a deep approach to learning is self-determined motivation, followed by evaluativism, and that the weakest factor is perceived social support, which is nevertheless a significant factor. Controlled motivation was found to have a weak negative effect. Mediation analyses, with self-determined motivation as a mediator, show the existence of both direct and indirect significant effects of evaluativism and perceived social support on deep approach to learning. These findings have important educational implications in that they help to identify key levers that teachers can activate to engage their students in deeper learning.