Accurate and appropriate cognitive screening has the potential to significantly enhance early psychosis care, yet no screening tools have been validated for the early psychosis population and little is known about current screening practices, experiences, or factors that may influence implementation. Using a hybrid type 1 design, the CogScreen study aims to validate two promising screening tools with young people with first episode psychosis (primary aim) and to understand the context for the implementation of cognitive screening in early psychosis settings (secondary aim). The present protocol outlines the implementation study, which aims to explore the experiences and practices, acceptability, feasibility, and determinants of cognitive screening in early psychosis settings from the perspective of key stakeholders. Young people with first episode psychosis (n=350), caregivers (minimum n=10), and service providers (minimum n=12) will be recruited from primary and specialist early psychosis services in Melbourne, Adelaide, and Sydney, Australia. Grounded in implementation science, two theoretical frameworks inform data collection and analysis: the Theoretical Framework of Acceptability and the Consolidated Framework for Implementation Research. A mixed methods design will be employed to collect and analyse data from questionnaires with young people with first episode psychosis, interviews with all stakeholder groups, and administrative processes. Quantitative data will be analysed using descriptive statistics. Qualitative data will be analysed through content analysis using deductive and inductive coding. Together with accuracy findings, results from the present implementation study will provide new insights about the practices, experiences, enablers and barriers to cognitive screening in early psychosis services.