Mererid is a Clinical Professor at the Division of Cancer and Genetics, School of Medicine, Cardiff University and an Honorary Consultant Clinical Oncologist at Velindre Cancer Centre, specialising in the management of patients with head and neck cancer. She is Director of the Wales Cancer Research Centre, a Health and Care Research Wales funded infrastructure that supports cancer research across Wales. In her role as Velindre Cancer Research Strategy Clinical Lead she leads Velindre’s involvement in the Cardiff Cancer Research Hub (CCRH), a partnership with Cardiff University and Cardiff and Vale Health Board to deliver novel cancer treatments and drive translational cancer research in Wales. She is Chief Investigator of two clinical trials aiming to develop kinder treatments for patients with Human Papillomavirus (HPV)-positive head & neck cancer: 1) PATHOS, a Cancer Research UK funded international phase III randomised trial of de-intensified adjuvant radiotherapy after transoral surgery and 2) PEARL, a Cancer Research Wales funded multi-centre trial of FDG-PET-based Adaptive Radiotherapy (ART). She is also co-investigator of PROTIS, a randomised trial of proton beam and photon RT for sinonasal cancers (led by Manchester) and RAPTOR, a randomised trial of PENTOCLO in mandibular osteoradionecrosis (led by Liverpool University). Internationally, she Chaired the American Joint Committee on Cancer (AJCC) Expert Panel on HPV-Associated Oropharyngeal Cancer staging, and represented the European Society for Radiotherapy and Oncology (ESTRO) as Chair of the International Congress on Innovative Approaches in Head and Neck Oncology in 2024 and 2026.