This study is a randomized controlled trial of an asynchronous, fully web-based program for divorced and separated parents, the electronic New Beginnings Program (eNBP). This program is an adaptation of a group, in-person program for divorced parents, the New Beginnings Program (NBP), which has been shown in randomized trials to reduce a wide range of offspring problems and improve a wide range of competencies up to 15 years after participation. The 10-module, 5-h program uses evidence-based, highly interactive strategies to teach skills designed to strengthen parenting after divorce and reduce interparental conflict. Participants were 131 parents (63% mothers) and 102 adolescent offspring. Parents were randomly assigned to the eNBP or a wait-list control condition. Parents and their children completed pre- and post-tests. Analyses showed that at post-test, parents and children in the eNBP reported significantly higher parent–child relationship quality, more effective discipline, lower interparental conflict and lower child mental health problems than did those in the wait-list control condition. These are the strongest findings in the literature on the effects of web-based programs to reduce interparental conflict, strengthen positive parenting and reduce children’s post-divorce mental health problems. Given that parental divorce has significant individual and societal costs, widespread implementation of this program could have significant public health implications.