Background Intravenous thrombolysis is a key element of emergency treatment for acute ischaemic stroke, but hospital service delivery is variable. The Paramedic Acute Stroke Treatment Assessment (PASTA) multicentre cluster randomised controlled trial evaluated whether an enhanced paramedic-initiated stroke assessment pathway could improve thrombolysis volume. This paper reports the findings of a parallel process evaluation which explored intervention paramedics' experience of delivering the enhanced assessment. Methods Interviewees were recruited from 453 trained intervention paramedics across three UK ambulance services hosting the trial: North East, North West and Welsh Ambulance Services. A semistructured interview guide aimed to (1) explore the stroke-specific assessment and handover procedures which were part of the PASTA pathway and (2) enable paramedics to share relevant views about expanding their role and any barriers/enablers they encountered. Interviews were audiorecorded, transcribed verbatim and analysed following the principles of the constant comparative method. Results Twenty-six interviews were conducted (11 North East, 10 North West and 5 Wales). Iterative data analysis identified four key themes, which reflected paramedics' experiences at different stages of the care pathway: (1) Enhanced assessment at scene: paramedics felt this improved their skillset and confidence. (2) Prealert to hospital: a mixed experience dependent on receiving hospital staff. (3) Handover to hospital team: standardisation of format was viewed as the primary benefit of the PASTA pathway. (4) Assisting in hospital and feedback: due to professional boundaries, paramedics found these aspects harder to achieve, although feedback from the clinical team was valued when available. Conclusion Paramedics believed that the PASTA pathway enhanced their skills and the emergency care of stroke patients, but a continuing clinical role postadmission was challenging. Future studies should consider whether interdisciplinary training is needed to enable more radical extension of professional boundaries for paramedics.