This study assessed whether elevated levels of maternal stress and anxiety and disturbed maternal sleep would be associated with greater negative infant temperament. The study was part of a larger longitudinal observational study investigating whether sleep-wake and gut microbiome development are associated with infant rapid weight gain in their first year. The present study focused on data from 43 mother-infant dyads collected at six months postpartum using the Depression and Anxiety Stress Scales (DASS), maternal wrist actigraphy sleep data (for five days and nights), maternal sleep diaries, the Pittsburgh Sleep Quality Index (PSQI), and the Infant Behavior Questionnaire-Revised (IBQ-R) very short form. While controlling for maternal age and anxiety, regression analyses revealed that lower actigraphy-assessed maternal sleep efficiency predicted greater infant negative affect, and greater actigraphy-assessed maternal total sleep time predicted lower infant surgency at six months. Maternal stress and anxiety were not significantly associated with infant temperament. This secondary study adds value to the literature with the inclusion of objective measurement of maternal sleep and consideration of other dimensions of maternal psychological distress that were previously highly examined in the scientific literature.