Introduction: Early intervention Services (EIS) in psychosis are the gold standard to treat patients after a first episode of psychosis (FEP). However, the understanding of the evolution and the long-term effects of such type of intervention is limited. This study aims to gain insight into the long-term evolution of physical and mental health, as well as the neurobiological outcomes of the patients treated for a FEP. Methods: The Long-term Follow-up of TIPP (LOFT) is an up to 20-year study within a cohort of patients who completed a three-year EI treatment at Treatment and early Intervention in Psychosis Program (TIPP, in Lausanne, Switzerland) and went through a deep phenotyping prospective multimodal assessment. 720 patients will be contacted and asked to participate in LOFT. Once they are assessed they will be allocated to a timepoint at either 5(+2), 10(±2), 15(±2), and 20(-2) years after TIPP entry. A follow-up visit will be proposed every 5 years. All participants will be evaluated on psychopathological, functional, and physical health outcomes including metabolic disturbances. A subsample of the patients who previously took part in a biomarker research program (n = 168) whilst at TIPP will be invited to undergo additional assessments (cognition, brain imaging, biofluids collection). Both traditional group level and machine learning analyses will be conducted. Conclusion: Ethical approval has been obtained and recruitment started in 2024. LOFT will help reshape and redefine current interventions for subgroups of patients at risk of poorer long-term outcome and to understand the underlying neurobiological mechanisms influencing psychosis evolution.