Effortful control (EC) refers to the ability to inhibit a dominant response to perform a subdominant one and has been shown as protective against a myriad of difficulties. Research examining precursors of EC has been limited to date, and in this study, infancy contributors to toddler EC were examined. Specifically, parent/family background variables (e.g., education, income), maternal temperament, perceived stress, and internalizing symptoms were addressed, along with infant temperament: positive affectivity/surgency (PAS), negative emotionality (NE), and regulatory capacity/orienting (RCO); and laboratory observation-based indicators of attention. Infant attention indexed by the latency to look away after initially orienting to the presented stimuli emerged as an important predictor of later EC, after accounting for other child and parent/family attributes, with shorter latencies predicting higher levels of EC. Mothers’ extraversion and parenting stress were the only parent/family attributes to significantly contribute to the prediction of toddler EC, with the former promoting and the latter undermining the development of EC. Infant temperament factors were also examined as a moderator of parent/family influences, with results indicating a significant interaction between mothers’ EC and infant RCO, so that children with greater RCO and mothers high in EC exhibited the highest EC scores in toddlerhood.