Background: To investigate potential facilitators and barriers for patients receiving specialised mental healthcare using a longitudinal design. Methods: Longitudinal data on 701 adult participants with a depressive and/or anxiety disorder were derived from the Netherlands Study of Depression and Anxiety (NESDA). Demographic, clinical and treatment determinants at baseline were assessed with self-report questionnaires and the Composite International Diagnostic Interview (CIDI 2.1). Transition to specialised mental healthcare was assessed at one, two, four, and six-year follow-up with a self-report resource use questionnaire (TiC-P). Results: 28.3% of patients with a depressive and/or anxiety disorder transitioned from receiving no care or primary mental healthcare to specialised mental health services during six-year follow-up. The multivariate Cox regression model identified suicidal ideation, younger age, higher education level, openness to experience, pharmacological treatment, prior treatment in primary mental healthcare and perceived unmet need for help as determinants of transition, explaining 8–18% of variance. Limitations: This study focused on baseline determinants of future transition to specialised mental healthcare. Recovery and remittance of depression and anxiety in relation to transition were not studied. Conclusions: Not all key clinical guideline characteristics such as severity of symptoms and comorbidity were predictive of a transition to specialised mental healthcare, while non-clinical factors, such as age and perceived unmet need for help, did influence the process.