There is growing evidence of the relationship between Metabolic Syndrome (MetS) and cognitive decline; however, this has not been conclusively established yet. This systematic review and meta-analysis address the most crucial cognitive performance findings, including those on global cognitive function, memory, attention, and executive functions, in adult people with MetS. Two electronic databases were searched (April-May 2020) using the terms "metabolic syndrome" and "cognition," including publications from 2010 to 2020. Thirty-six studies were found. Among these, 17 reported negative associations in cognition with MetS, mainly in terms of verbal memory and executive functions, particularly in the middle-aged population. A meta-analysis of global cognitive function revealed that the MetS group had a lower score than the control group (25.26 and 25.6, respectively, 95% CI, −0.60 to −0.12, p = 0.004). MetS is related to the enhanced presentation of cognitive impairment and its evolution into a Major Neurocognitive Disorder (MND). Further research involving longitudinal studies, including assessments with similar instruments, correctly separated by age group and education, is required.