Objective Promoting adherence to healthy dietary patterns is a critical public health issue. Models of behaviour, such as the Theory of Planned Behaviour (TPB) allow programme designers to identify antecedents of dietary patterns and design effective interventions. The primary aim of this study was to examine the association between TPB variables and dietary patterns. Methods A systematic literature search was conducted to identify relevant studies. Random-effects meta-analysis was used to calculate average correlations. Meta-regression was used to test the impact of moderator variables. Results In total, 22 reports met the inclusion criteria. Attitudes had the strongest association with intention (r+ = 0.61) followed by perceived behavioural control (PBC, r+ = 0.46) and subjective norm (r+ = 0.35). The association between intention and behaviour was r+ = 0.47, and between PBC and behaviour r+ = 0.32. Moderator analyses revealed that younger participants had stronger PBC–behaviour associations than older participants had, and studies recording participants' perceptions of behaviour reported significantly higher intention–behaviour associations than did those using less subjective measures. Conclusions TPB variables were found to have medium to large associations with both intention and behaviour that were robust to the influence of key moderators. Recommendations for future research include further examination of the moderation of TPB variables by age and gender and the use of more valid measures of eating behaviour.