Background This study tested whether video‐feedback intervention based on attachment and coercion theory increased harmonious parent–child interaction and sensitive discipline of parents with mild intellectual disabilities or borderline intellectual functioning. Methods Observer ratings of video‐recorded structured interaction tasks at home formed pretest, post‐test, and 3‐month follow‐up outcome data in a randomized controlled trial with 85 families. Repeated measures analyses of variance and covariance were conducted to test for the intervention effect and possible moderation by IQ and adaptive functioning. Results The intervention effect on harmonious parent–child interaction was conditional on parental social adaptive behaviour at pretest, with lower adaptive functioning associated with stronger intervention benefit at post‐test and follow‐up compared to care as usual. Intervention effects were not conditional on parental IQ. Intervention effects for sensitive discipline were not found. Conclusion Although the video‐feedback intervention did not affect observed parenting for the average parent, it may benefit interaction between children and parents with lower parental adaptive functioning.