Background: There are increasing rates of university students with mental health issues, including stress, anxiety, depression, and mood disorders. Dietary (poly)phenols, bioactive compounds found in plant-based foods are emerging as potential modulators of mental well-being, possibly through a mechanism involving gut microbiota interactions. Objectives: To examine the associations between (poly)phenol intake, circulating (poly)phenol metabolites and mental health in university students. Methods: A cross-sectional study was conducted from September 2022 to June 2024 at King’s College London including 307 healthy university students aged 17-30 years. Participants completed validated 24-hour dietary recalls for 3 days using online Intake24 and the KCL (poly)phenol food frequency questionnaire (KP-FFQ). (Poly)phenol intake was quantified using an in-house database based on Phenol-Explorer and USDA databases. Mood, stress, anxiety and depression outcomes were assessed using the Profile of Mood States 2nd Edition–Adult (POMS 2-A), Perceived Stress Scale (PSS), and Hospital Anxiety and Depression Scale (HADS), respectively. A total of 114 (poly)phenol metabolites were quantified in 24 h urine samples by Liquid Chromatography-Mass Spectrometry using a validated method. Generalized Linear Model analysis was conducted to examine the association between (poly)phenol intake and mental health. Results: A higher consumption of anthocyanins associated with lower anxiety and stress (p <0.01); higher intake of flavanones with lower depression and mood (p< 0.05); higher flavonols intake with lower anxiety, depression and stress (p< 0.05); higher tyrosols and lower all four outcomes (p< 0.001) after full adjustment for potential confounding factors. Additionally, higher flavan-3-ol consumption was associated with lower cortisol levels (p< 0.05), and urinary (poly)phenol metabolites were significantly associated with mental health outcomes (p< 0.05). Conclusion: The findings suggest that consumption of anthocyanins, flavanones, flavonols and tyrosols, are associated with a lower prevalence of mental health symptoms among university students, including lower cortisol levels. Further studies are needed to confirm these associations.