Emotional mimicry, the tendency to automatically and spontaneously reproduce others’ facial expressions, characterizes human social interactions from infancy onwards. Yet, little is known about the factors modulating its development in the first year of life. This study investigated infant emotional mimicry and its association with parent emotional mimicry, parent-infant mutual attention, and parent dispositional affective empathy. One hundred and seventeen parent-infant dyads (51 six-month-olds, 66 twelve-month-olds) were observed during video presentation of strangers’ happy, sad, angry, and fearful faces. Infant and parent emotional mimicry (i.e., facial expressions valence-congruent to the video) and their mutual attention (i.e., simultaneous gaze at one another) were systematically coded second-by-second. Parent empathy was assessed via self-report. Path models indicated that infant mimicry of happy stimuli was positively and independently associated with parent mimicry and affective empathy, while infant mimicry of sad stimuli was related to longer parent-infant mutual attention. Findings provide new insights into infants’ and parents’ coordination of mimicry and attention during triadic contexts of interactions, endorsing the social-affiliative function of mimicry already present in infancy: emotional mimicry occurs as an automatic parent-infant shared behavior and early manifestation of empathy only when strangers’ emotional displays are positive, and thus perceived as affiliative.