The mental health liaison nurse role in the emergency department (ED) has demonstrated a range of positive outcomes for both consumers and staff. In Australia, the added value associated with establishing mental health nurse practitioner (MHNP) positions based on this model is emerging. This paper presents qualitative findings from a study using a mixed-method design to evaluate an ED-based MHNP outpatient service in Sydney, Australia. In evaluating this new service, semistructured interviews were conducted with a random selection of study participants and a stratified sample of ED staff. This is the first of a two-part paper that presents an analysis of qualitative data from interviews conducted with study participants (n = 23). Participants reported numerous therapeutic benefits from the service, such as support, understanding, and a focus on solutions rather than problems, and high levels of satisfaction with the accessibility of the service and follow up. Suggestions for improving the service were also offered. Participants emphasized that overall ED service provision would be enhanced through additional resources, especially an extension of operating hours. Findings from these participant interviews provide strong support for an ED-based MHNP outpatient service.