Objective: It is well established that cognition is associated with everyday functioning. This study sought to determine the strength of the relationship between cognition and functional outcomes in a sample of mild cognitive impairment (MCI). Method: A meta-analysis based on 98 papers, with 132 study samples, involving 18,069 individuals with MCI was conducted. Potential demographic (i.e., age and education), clinical (i.e., MCI subtype and referral source), and methodological moderators (i.e., cognitive and functional status domains and subdomains) were also examined. Results: Overall analysis revealed that cognition explained an average of 23% of the variance in functional outcomes. Effect sizes for cognitive domains and subdomains were in the medium to large range. Executive function measures, and Trails B in particular, explained the largest amount of variance (37%) in functional abilities while speeded processing and global cognitive measures explained the least (20%). Delayed memory measures also accounted for significantly more variance in functional outcomes than immediate memory measures, and the relationship between cognition and functional outcomes was stronger when assessed with informant-report compared to self-report. Demographics, sample characteristics, and the measures used to assess everyday functioning explained relatively little variance compared to cognition. Conclusion: A better understanding of the cognitive and noncognitive correlates of everyday functioning in MCI is needed and could have important clinical and research applications for the improvement and stability of diagnosis and development of interventions. Areas for future research are discussed.