Background Anxiety disorders tend to precede onset of comorbid depression. Several researchers have suggested a causal role for anxiety in promoting depressive episodes, but few studies have identified specific mechanisms. The current study proposes an interpersonal model of comorbidity, where anxiety disorders disrupt interpersonal functioning, which in turn elevates risk for depression. Methods At age 15 (T1), 815 adolescents oversampled for maternal depression completed diagnostic interviews, social chronic stress interviews, and self‐report measures. At age 20 (T2), participants repeated all measures and reported on self‐perceived interpersonal problems. At approximately age 23 (T3), a subset of participants (n = 475) completed a self‐report depressive symptoms measure. Results Consistent with other samples, anxiety disorders largely preceded depressive disorders. Low sociability and interpersonal oversensitivity mediated the association between T1 social anxiety disorder and later depression (including T2 depressive diagnosis and T3 depressive symptoms), controlling for baseline. Interpersonal oversensitivity and social chronic stress similarly mediated the association between generalized anxiety disorder before age 15 and later depression. Conclusions Interpersonal dysfunction may be one mechanism through which anxiety disorders promote later depression, contributing to high comorbidity rates.