Background Prior research has shown that the Sadness Program, a technician‐assisted Internet‐based cognitive behavioral therapy (iCBT) intervention developed in Australia, is effective for treating major depressive disorder (MDD). The current study aimed to expand this work by adapting the protocol for an American population and testing the Sadness Program with an attention control group. Methods In this parallel‐group, randomized controlled trial, adult MDD participants (18–45 years) were randomized to a 10‐week period of iCBT (n = 37) or monitored attention control (MAC; n = 40). Participants in the iCBT group completed six online therapy lessons, which included access to content summaries and homework assignments. During the 10‐week trial, iCBT and MAC participants logged into the web‐based system six times to complete self‐report symptom scales, and a nonclinician technician contacted participants weekly to provide encouragement and support. The primary outcome was the Hamilton Rating Scale for Depression (HRSD), and the secondary outcomes were the Patient Health Questionnaire‐9 and Kessler‐10. Results Intent‐to‐treat analyses revealed significantly greater reductions in depressive symptoms in iCBT compared with MAC participants, using both the self‐report measures and the clinician‐rated HRSD (d = −0.80). Importantly, iCBT participants also showed significantly higher rates of clinical response and remission. Exploratory analyses did not support illness severity as a moderator of treatment outcome. Conclusions The Sadness Program led to significant reductions in depression and distress symptoms. With its potential to be delivered in a scalable, cost‐efficient manner, iCBT is a promising strategy to enhance access to effective care.