The Unified Protocol (UP) as a transdiagnostic intervention has primarily been applied in the treatment of anxiety disorders and in face-to-face-settings. The current study investigated the efficacy of a 10-week internet-based adaptation of the UP for anxiety, depressive, and somatic symptom disorders. N=132 participants were randomized to treatment or waitlist control. Linear mixed effect models revealed significant treatment effects for symptom distress, satisfaction with life, positive/negative affect and markers of anxiety, depression, and somatic symptom burden (within-group Hedges’ g = 0.32-1.38 and between-group g = 0.20-1.11). Treatment gains were maintained at 1- and 6-month-follow-up. Subgroup analyses showed comparable effects in participants with anxiety and depressive disorders. The results strengthen the application of the UP as an internet-based treatment for alleviating symptom distress across emotional disorders. More research on the applicability for single disorders and the mechanisms underlying the effects is needed.