Mindfulness-based interventions (MBIs) are commonly used for cancer patients and survivors to reduce symptoms, but little is known about effects on positive health outcomes. We conducted a systematic review and meta-analysis to determine the effects of MBIs on positive health outcomes (mindfulness skills, self-compassion, positive affect, coping, social support, well-being, personal growth, and spirituality) in cancer patients and survivors. Four databases (PubMed, PsycINFO, Web of Science, and CINAH) were searched (grey literature was not included), abstracts and full texts were screened, and MBI quality and risk of bias were assessed. Effect sizes were calculated and data was analyzed using a frequentist analytical strategy. Eligible studies were randomized controlled trials (RCTs) evaluating the effect of MBIs compared to any type of control on positive health outcomes in cancer patients or survivors. Based on 46 RCTs eligible for meta-analysis, statistical significant effects were observed for all positive health outcomes at post-treatment. Effect sizes ranged from small (positive affect; Hedges's g = 0.26) to large (spirituality, g = 0.91). At follow-up, mindfulness skills, self-compassion, personal growth, and spirituality reached statistical significance, with effect sizes ranging from small (positive affect; g = 0.07) to medium (spirituality; g = 0.61) and large (post-traumatic growth; g = 1.40). Taken together, significant effects of MBIs were found for several positive outcomes in cancer patients and survivors, with the strongest evidence found for mindfulness skills. MBIs may play a key role in improving well-being in this population.