This systematic review and narrative synthesis characterized parents\' physiological stress responses to child distress and how parents\' physiological and behavioural responses relate. The review was pre-registered with PROSPERO (#CRD42021252852). In total, 3607 unique records were identified through Medline, Embase, PsycINFO, and CINAHL. Fifty-five studies reported on parents\' physiological stress responses during their young child\'s (0-3 years) distress and were included in the review. Results were synthesized based on the biological outcome and distress context used and risk of bias was evaluated. Most studies examined cortisol or heart rate variability (HRV). Small to moderate decreases in parents\' cortisol levels from baseline to post-stressor were reported across studies. Studies of salivary alpha amylase, electrodermal activity, HRV, and other cardiac outcomes reflected weak or inconsistent physiological responses or a paucity of relevant studies. Among the studies that examined associations between parents\' physiological and behavioural responses, stronger associations emerged for insensitive parenting behaviours and during dyadic frustration tasks. Risk of bias was a significant limitation across studies and recommendations for future research are discussed.