BackgroundProgrammes for early intervention (EIP) in psychosis for people experiencing a first episode of psychosis (FEP) have been found to be both clinically and cost effective. Following the publication of a new EIP model of care (MoC) in Ireland, the aim of this research is to describe how people participated in and responded to the MoC including service users, family members, HSE clinical staff and HSE management.MethodsQualitative design using the UK Medical Research Council’s process evaluation framework. Purposive sampling techniques were used. A total of N = 40 key informant semi-structured interviews were completed which included clinical staff (N = 22), health service managers and administrators (N = 9), service users (N = 8) and a family member (N = 1). Thematic analyses were conducted.ResultsUnique features of the EIP service (e.g., speed of referral/assessment, multidisciplinary approach, a range of evidence-based interventions and assertive MDT follow up) and enthusiasm for EIP were identified as two key factors that facilitated implementation. In contrast, obstacles to staff recruitment and budget challenges emerged as two primary barriers to implementation.ConclusionsThe findings from this research provide real world insights into the complexity of implementing an innovative service within an existing health system. Clear and committed financial and human resource processes which allow new innovations to thrive and be protected during their initiation and early implementation phase are paramount. These elements should be considered in the planning and implementation of EIP services both nationally in Ireland and internationally.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12913-023-09585-3.