Significance Metastasis is the most common cause of cancer-related death. The function of reactive oxygen species (ROS) in metastasis is conflicting, and it has been observed to promote or inhibit metastasis. Thus, a more in-depth analysis is needed to assess the impact of ROS on metastasis. In this study, we find that local down-regulation of SIRT3 at the leading edge of migrating cells results in elevated ROS levels and activation of Src/focal adhesion kinase signaling. Further, collective cell migration and metastases formation are inhibited by SIRT3, while patient data sets point to an inverse correlation between SIRT3 and breast cancer metastasis.