This study examined parental romantic attachment security as a mediator of prospective associations between hostile interparental conflict and parental discipline (i.e., power-assertive, permissive, and inductive discipline) for mothers and fathers of young children. Furthermore, this study utilized a novel, automatic assessment of romantic attachment security in examining whether romantic attachment assessed at controlled (i.e., self-reported) and automatic (i.e., a rapid word-sorting task) levels of representation differentially serve as spillover mechanisms. Participants included 235 mothers (62% White), fathers (55% White), and a target child between the ages of 2 and 4 (Mage = 2.97; 55% girls) recruited from a moderate-sized metropolitan area in the Northeastern United States. Families were assessed annually across three waves of data collection. Results from autoregressive structural equation model analyses revealed that romantic attachment operated as spillover mechanism for mothers. In particular, hostile interparental conflict was associated with power-assertive discipline through changes in mothers' automatic romantic attachment security. We also found that hostile interparental conflict was associated with inductive discipline through changes in mothers' romantic attachment avoidance. Neither controlled nor automatic romantic attachment representations served as spillover mechanisms for fathers. Findings are discussed within family systems and attachment frameworks. (PsycInfo Database Record (c) 2024 APA, all rights reserved).