Postnatal depression (PND) confers risk for a range of negative child developmental outcomes, at least in part through its impact on parenting behaviour. Whilst the behavioural effects of depression on parenting are well established, the cognitive mechanisms that may mediate this effect are less well understood. The current paper proposes that rumination may be a key cognitive mechanism through which parenting is affected in PND, and provides a systematic review of the existing literature on rumination in the context of perinatal depression. The review identifies ten relevant papers. Eight are questionnaire-based studies examining the role of rumination in predicting future depression and/or mother-infant relationship outcomes, such as bonding. Two are experimental studies examining the effects of induced rumination on parenting behaviours. The results of the review are discussed, and remaining questions highlighted. We then present a new theoretical model, developed specifically for the perinatal context, and informed by existing models of rumination and worry. Our cognitive model emphasises the relationship between rumination, cognitive biases and cognitive control, and the impact of these variables on infant cue processing and subsequent parenting responses. The model provides a potential framework for future work in this area, and to guide the development of treatment interventions.