Models of perfectionism and stress have become increasingly complex, yet perseverative cognition has been largely absent from these models and remains under-represented in the perfectionism and stress literature. This research makes several key advances by testing the perseverative cognition hypothesis in relation to perfectionism and daily stress in a community sample of 100 working professionals. We collected data over a 7-day period using a multi-method daily diary design including self-report measures of daily experiences and daily heart rate variability (HRV), which is thought to reflect physiological adaptation to stress. HRV was measured daily using 15-min samples at the end of each day. Data were aggregated across days and analyzed using path analysis. Results showed self-critical perfectionism predicted poorer adaptation to stress directly and indirectly through perseverative cognition pathways (i.e., the combined effect of daily stress and event-focused rumination). However, considering the impact of daily stress alone did not show detrimental effects on HRV. Perfectionistic strivings was not related to perseverative cognition pathways, but it showed a small positive direct effect on HRV. Findings highlight perseverative cognition as a useful framework for understanding perfectionism and physiological adaptation to stress, and this research points toward the development of an integrative bio-psycho-social model of perfectionism and stress vulnerability.