This study evaluated how patterns of mothers’ depressive symptoms across their child’s childhood relate to children’s psychosocial adjustment at adolescence and young adulthood and to cognitive functioning at adolescence. Depressive symptoms were measured in 1273 mothers when their children were 1, 5, 10, and 14.6 years of age. Children (53.5% male; n = 1024) completed the Youth Self-Report at adolescence (M = 14.6 y), and the Adult Self-Report in young adulthood (M = 20.5 y; n = 817) to assess internalizing and externalizing symptoms. Adolescents also completed standardized cognitive tests to assess verbal and mathematical skills. Growth mixture modeling analyses identified four patterns of maternal depressive symptom trajectories: infrequent (55%), increasing at adolescence (20%), decreasing at adolescence (14%), and chronic severe (11%). Results indicated that exposure to maternal depression of any duration, severity or time period during childhood portended higher levels of externalizing and attention problems at both adolescence and adulthood and higher levels of internalizing problems at adulthood. Adolescents whose mothers had chronic severe depressive symptoms had lower language, vocabulary, reading comprehension and mathematical test scores than youth whose mothers had stable infrequent depressive symptoms. Findings illustrate the significance and long-term ramifications of mothers’ depressed mood for their children’s mental and psychosocial health into adulthood. Findings also demonstrate that the lower cognitive abilities among children of severely depressed mothers persist beyond childhood and pertain to a broad range of cognitive abilities.