Numerous consumers engage in wasteful and unsustainable consumption despite knowing it is associated with several personal, social, economic, and environmental harms. To aid consumers in reducing consumption, we created Breaking up with Belongings (BB), a fully automated web-based intervention with a downloadable workbook. Eligible participants were recruited using social media ads. They were Australian residents, aged 18 or older, fluent in English, had consistent computer and internet access, and reported having excess possessions and/or having difficulty making intentional decisions about possessions. We assessed the feasibility, acceptability, and preliminary efficacy of this intervention compared to a waitlist (WL) control in a 3-month, parallel, two-arm pilot randomized controlled trial. Over three weeks, 171 individuals screened for this study; 96 were eligible and randomized to condition (48 BB group, 48 WL group). Three-quarters of participants provided follow-up data and accessed the program. The BB group found the program acceptable and outperformed the WL group on two primary outcomes (cautious shopping and clutter removal) and on all secondary outcomes (impulsive buying, expenditure, hoarding tendencies, clutter-related impairment, object attachment, and emotion regulation). These findings will be used to enhance the program’s effectiveness and broader applicability, which will be tested through a larger randomized controlled trial.