Objective This study investigated the phases of change and the relationship between binge eating (BE) episodes and weight across 20 weeks of emotionally focused group therapy (EFGT) and combined therapy (CT) of EFGT plus dietary counselling for BE disorder. Methods We used a non‐randomized observational study design that included 118 obese adult patients with BE disorder who were treated by manualized therapy protocols. Participants were assigned to treatment condition (EFGT or CT) based on consensus among clinicians. Participants were assessed weekly during the 20 weeks of therapy for weight and BE episodes and at pre‐treatment and 6 months post‐treatment. Results Binge eating episodes and weight significantly declined during EFGT and CT. Compared with EFGT, CT resulted in more rapid weight loss across weeks of therapy. BE episodes and weight significantly covaried, and their positive association increased as sessions progressed. Change in BE episodes and weight during treatment was best modelled by a cubic growth curve showing a slow rate of change in early sessions, a faster rate of change in middle sessions and a slower rate of change in late sessions. This cubic modelling of change was associated with better outcomes 6 months post‐treatment. Conclusion Cubic modelling of change supported a three‐stage model of EFGT and CT, and the cubic trajectory was associated with better outcomes at follow‐up. The addition of dietary counselling to EFGT resulted in earlier response to treatment in terms of BE episodes and weight among those in the CT condition. Key Practitioner Message Decline in binge eating (BE) episodes is related to decline in weight, and this relationship was greater towards the end of treatment.Emotionally focused group therapy plus dietary counselling that targets both affect regulation and nutritional problems resulted in faster rate of response early in treatment both in terms of BE episodes and weight.Combined emotionally focused group therapy and dietary counselling may provide clinicians with an additional approach to treating BE disorder. Copyright © 2014 John Wiley & Sons, Ltd.