Introduction: The need to improve quick access to effective psychological treatments is urgent. Success requires effective tools for identifying what kind of therapies an individual is likely to benefit from and managing a comprehensive therapy offering that matches an individual’s needs. First-line therapies initiative (Terapiat etulinjaan–toimintamalli) is a national initiative started 2020 in Finland. It aims to help Finnish regions in building locally sustainable stepped care systems and providing the support services needed. One key service of First-line therapies initiative is the Finnish therapy navigator (FTN). The FTN is a digital tool to help assess individual needs for psychosocial treatments and to build a regionally sustainable stepped care treatment offering, as part of the national reform of social and health services. This paper describes the development, content, implementation and feasibility of the FTN. Materials and Methods: The system was piloted in six regions in Finland between October 2021 and May 2022, with a catchment area of around 600 000. The feasibility data was collected from professionals (n = 48) using the system at 1 and 4 months after implementation, and from the anonymous FTN responses (n = 2630). Results: Professionals estimated the FTN had a positive impact on their work, quality of assessment and notes, and patient experience at 1 month after starting to use the FTN. Satisfaction scores improved further at 4 months, and 93% of users wanted to keep FTN as a permanent tool. The mean time patients used to fill the FTN was 24 minutes; 75% of clinical interviews lasted under 30 minutes. The FTN provides important data on treatment seekers. In our sample 57% of respondents scored between 10-19 points on PHQ-9 and 59% between 5-14 on GAD-7, suggesting mild-to-moderate depressive and anxiety symptoms. 28% reported no previous psychosocial treatments and 33% previous treatments shorter than 6 months. Thus, it seems that a significant proportion of treatment seekers in Finland could benefit from readily available, short-term, evidence-based psychosocial treatments that the First-line therapies initiative supports. Conclusions: FTN is a feasible tool for first assessment of mental health issues in primary care. Implemented and localized using the manualized co-creation process results in very high user satisfaction and acceptability of the system. The FTN provides important real-time data on mental health treatment seekers to support service development and planning. The First-line therapies model that includes introducing FTN in combination with regionally adapted care pathway development, education in short evidence-based psychological interventions and increase in use of digital support systems appears a feasible way to build regionally sustainable stepped systems.