<p>Limiting global warming to 1.5 ℃ requires systemic changes, including shifts in consumption patterns. Mobile applications can support individuals in adopting sustainable consumption practices by providing guidance, information and interventions. This study investigates the greenhouse gas emissions reduction potential of a mobile application and examines how it encouraged individuals to seek sustainable lifestyles using data from the Climate Campaigners research project (<i>n</i> = 6,240). The studied mobile app suggested sustainable lifestyle interventions called ‘challenges’, which were designed to reduce the app user’s personal carbon footprint and to help them adopt sustainable lifestyle changes. The results show that app users were more successful in completing short-term (one week or less), low emission impact lifestyle challenges than long-term (one month or a year), high emission impact challenges. Easiness was the main reason for completing a challenge in all the lifestyle categories reviewed. Although the number of completed challenges was higher for low emission impact challenges, high emission impact and long-term challenges had greater emission reduction potential. If short-term and low emission impact challenges become part of users’ daily habits, the emission reduction potential of these challenges may increase. However, if the continuity of using the app ceases, the probability of achieving substantial emissions reductions remains uncertain. The impact of sustainability-related mobile applications on emissions reductions depends significantly on user engagement and activity. These findings contribute to our understanding of the emission reduction potential of individual use of a mobile application and suggest that future research should focus on tracking the repetition of short-term challenges, understanding how the continuity of long-term lifestyle changes can be supported and exploring the reasons why lifestyle changes are not completed.</p>