INTRODUCTION Health and social care professionals (HSCPs) have increasingly contributed to enhance the care of patients in emergency departments (EDs), particularly for older adults who are frequent ED attendees with significant adverse outcomes. For the first time, the effectiveness of a HSCP team intervention for older adults in the ED has been tested in a large randomised controlled trial (Clinicaltrials.gov, NCT03739515), providing an opportunity to explore the implementation process for this type of intervention. This protocol describes a process evaluation that will to investigate the implementation, delivery and impact of an HSCP team intervention in the ED. METHODS AND ANALYSIS Using the Medical Research Council Framework for process evaluations, we will employ a mixed-methods approach to provide a description of the process of implementation and delivery of the HSCP intervention in the ED, evaluate its fidelity, dose and reach and explore the perceptions of key staff members in relations to the mechanisms and contexts of impact at the levels of individuals, physical environment, operations, communication and the broader hospital and healthcare system. ETHICS AND DISSEMINATION Ethical approval for this study was received from the HSE Mid-Western Regional Hospital Research Ethics Committee (Ref: 103/18). All participants will be invited to read and sign a written consent form prior to participation. The results of this review will be disseminated through publication in a peer-review journal and presented at relevant conferences.