Objectives <p>Problematic smartphone use (PSU) has emerged as a public health concern. Mindfulness is a potentially protective factor in the context of PSU, but the nature of this relationship remains unclear. We conducted a meta-analysis of associations between mindfulness and PSU, and a systematic review to elucidate the <i>contexts</i> in which mindfulness may be most beneficial (moderation) and the <i>mechanisms</i> through which these benefits may occur (mediation).</p> Method <p>We searched six databases (CINAHL, ERIC, PsycInfo, Pubmed, Scopus, Web of Science) from inception to December 2024 and included peer-reviewed, English language studies that examined the association between PSU (including nomophobia) and mindfulness.</p> Results <p>Our search yielded 61 independent studies (<i>N</i> = 38,802). Most sampled young adults (67.21%) and employed cross-sectional designs (83.6%), and almost half (49.18%) were conducted in China. Using multilevel linear mixed-effects models, we found a significant medium population effect size between mindfulness and PSU (<i>r</i> = -0.30). Despite 45 studies testing moderation and/or mediation effects, there was little overlap in models tested. The association between mindfulness and PSU was mediated by many factors, including lower mental health symptoms, rumination, and experiential avoidance, and a greater sense of control. Mindfulness often, but not always, attenuated the association between PSU risk factors (e.g., stress, alexithymia) and PSU symptoms.</p> Conclusions <p>There is potential value in integrating mindfulness into current theories and treatments of PSU. However, researchers must employ more rigorous methods to capture the complex, dynamic nature of these constructs and do so with greater focus on core constructs that may explain this association.</p> <p><b>Preregistration</b> This study is not preregistered.</p>