Plant-based diets (PBDs) have gained popularity in recent years due to their co-benefits for human and planetary health. Although clinical guidelines now recommend well-balanced PBDs, it remains unclear how dietitians in the United Kingdom (UK) and Republic of Ireland (ROI) view such diets and their implementation in practice. This study aimed to evaluate the perspectives of registered dietitians (RDs) on the role of a whole food plant-based diet (WFPBD) in clinical practice. A cross-sectional online survey was conducted amongst RDs in the UK and ROI between September and November 2023. A total of 335 RDs participated in the survey. Most RDs (76%) agree that a well-planned WFPBD is suitable for all stages of life, with some (48%) expressing concerns over the risk of malnutrition and micronutrient deficiencies. Three-quarters of RDs (75%) incorrectly thought that plant protein is incomplete, necessitating protein combining. A WFPBD was on average ranked fourth out of 14 dietary strategies for managing some of the leading non-communicable diseases. Excluding dairy and eggs was the primary reason preventing RDs from personally adopting a WFPBD, whereas meal preparation and cost were the main barriers for their clients. The majority of RDs (79%) feel they did not receive sufficient education on WFPBDs, with 58% agreeing there are insufficient evidence-based resources available in their field. Only 33% feel supported when advocating for a WFPBD in their workplace. Although many RDs view WFPBDs as viable and clinically relevant, significant barriers to their implementation exist, underscoring the need for enhanced education and support.