The recent rise in maternal workforce participation has led to more research regarding the role of maternal employment for (early) childhood mental health. This systematic review with meta-analysis covers new evidence on the association of both variables. A systematic literature search was conducted. Studies had to compare children 0–7 years of age on the basis of their mothers’ employment status, working amount, employment duration, i.e., how long the mother had been back at work after birth, or timing of return to work. Child mental health was operationalized as behavior problems and prosocial behavior. Narrative and meta-analytic syntheses of evidence were conducted. Maternal employment was associated with more conduct problems but less internalizing behavior problems and anxious/depressed behavior in children; full-time employment was linked to more externalizing behavior problems and more hyperactivity/inattention. Longer employment duration was related to less (internalizing) behavior problems and more prosocial behavior but also more externalizing behavior problems. Narrative syntheses indicated early maternal return to work to be associated with more child externalizing behavior problems and less prosocial behavior. Whether maternal employment is associated with child mental health strongly depends on both variables’ operationalization. Especially part-time employment, longer employment duration, and return to work only after the first year postpartum may be beneficial for child mental health. Practical implications pertain to an expanded offer of family leave and the endorsement of maternal employment after the first year postpartum. Here, factors that may buffer the negative associations with full-time employment warrant consideration.