The family is regarded as a vital environment for early academic competence, as reflected in literacy and cognitive skills and self-regulation, as well as for behavioral development, which encompasses both prosocial and problem behavior. Extensive research has consistently supported the positive associations between marital adjustment, maternal involvement in early childhood education, and children’s development. However, few studies have examined the interaction of marital adjustment and maternal involvement on children’s outcomes and the indirect role of maternal involvement in the relations between marital adjustment and children’s academic and behavioral competence. The current research was conducted in three Chinese provinces. A total of 653 mothers of Chinese preschoolers (51.76% boys, Mage = 5.94, SD = 1.43) from 15 preschool classrooms participated in this study. The results showed that higher marital adjustment was associated with improvement in children’s literacy and cognition (β = 0.26, p < 0.001), self-regulation (β = 0.25, p < 0.001), and prosocial behavior (β = 0.18, p < 0.001), as well as a reduction in problem behavior (β = 0.21, p < 0.001). Maternal involvement did not facilitate or buffer the effects of marital adjustment and early academic and behavioral development. Marital adjustment may contribute to increasing maternal involvement and thus indirectly affect children’s academic and behavioral competence. These findings highlight the potential positive effects of marital adjustment and maternal involvement on preschoolers’ academic and behavioral competence and introduce a different perspective on the cultivation of supportive family environments.