Although inhibitory control (IC) is associated with children's positive adjustment, we know relatively little about factors underlying its development. We examined whether baseline and on‐task respiratory sinus arrhythmia [(RSA); a physiological measure of self‐regulation] and private speech (a behavioral measure of self‐regulation) interacted to confer differences on directly observed IC in 52 typically developing 4‐year olds. We found that baseline RSA moderated the association between private speech and IC, such that private speech positively predicted IC in children with relatively higher baseline RSA, but was unrelated to IC in children with relatively lower RSA. We also found that children with a concordant physiological‐behavioral pattern (i.e., high RSA and high private speech; low RSA and low private speech) had higher IC, higher effortful control, and lower negative emotionality than those with a discordant physiological‐behavioral pattern (i.e., high RSA and low private speech; low RSA and high private speech). Individual differences in physiological and behavioral self‐regulation indices may represent distinct regulation pathways that interact to confer differences in IC during the preschool years.