When Mary Cassatt exhibited her paintings of mothers and children in Paris in the late 1880s, critics sometimes dismissed them as mere "feminine" subjects, yet these works quietly challenged the boundaries of Impressionism and domestic portraiture. Baby in Dark Blue Suit, Looking Over His Mother's Shoulder stands out from this period for its unusual vantage point: the viewer sees the infant not from the front, but from behind, as he peers intently over his mother's shoulder. This perspective was rare in late nineteenth-century portraiture, and it drew attention to the private, almost secret world between child and mother—a relationship that Cassatt, herself childless, explored with unmatched empathy. The painting captures a fleeting moment: the baby, dressed in a tailored dark blue suit, twists in his mother's arms, his small hand gripping her shoulder for balance.

His gaze is turned away from us, suggesting curiosity about something just out of sight, while the mother's face is hidden, making her presence felt through posture and touch rather than expression. The brushwork is loose, especially in the rendering of the clothing and background, echoing the techniques of Impressionism but with a focus on intimacy rather than landscape or social spectacle. Unlike Renoir's more sentimental depictions of children, Cassatt's approach is unsentimental and direct, emphasizing the physicality and independence of the child. The precise provenance of Baby in Dark Blue Suit, Looking Over His Mother's Shoulder is not fully documented, a common situation for Cassatt's works from this period, many of which were sold directly to collectors in France and the United States.

The painting likely formed part of a series of mother-and-child studies Cassatt produced in the late 1880s, a time when she was at the height of her creative powers and exhibiting with the Impressionists. Today, the work is celebrated as a key example of Cassatt's ability to merge the formal innovations of Impressionism with the psychological insight of portraiture, securing her reputation as one of the movement's most original voices.