This study investigated how mothers’ working status directly and indirectly influences their infants’ development. The participants were 1,818 mothers with children aged 11 months to 18 months from the Panel Study on Korean Children. We categorized mothers into four groups according to their working status: consistent working, transition to working, transition to nonworking, and consistent nonworking. We found two competing mediating mechanisms through which mothers’ working status influences infant development. First, mothers’ consistent working and transition to working status had a positive influence on their mental health in terms of low depressive symptoms and high self-esteem, which in turn positively contributed to positive parenting style. Second, mothers’ consistent working and transition to working status had direct adverse effects on their parenting style. Positive parenting style contributed to infant development. We also found that mothers’ transition to working directly enhanced infant development.