Parents with substance use disorder have multiple risks affecting their parenting. Mental health problems and adverse childhood experiences (ACEs) with problems in emotion regulation and adult attachment insecurity may impair the early interaction with the infant. An intensive treatment programme, Holding Tight, has been developed in Finland since the 1990s. It integrates social work and psychological interventions with mental health prevention. The aim here was to evaluate changes in parenting and parental well-being from pretreatment to post-treatment and a 6-month follow-up. We further examined the moderating effects of parental ACEs and duration of treatment. Participants were 66 Finnish mothers and 23 fathers, 42.7% entering treatment prenatally and the rest postnatally with their infants (M age = 5.43 months, SD = 10.02). Parents completed standardized self-report questionnaires. The results show improvements in child involvement, maternal own attachment insecurity and depressive symptoms and emotion regulation. However, the results also show that mothers with higher ACEs had more depressive symptoms and showed more decrease during and more increase after treatment. Additionally, mothers with longer treatment showed more decrease in attachment anxiety and more increase in child involvement. We discuss how these results may bear significance in the future implementation of comprehensive treatment models.