As cognitive decline is a progressive process, it is crucial to determine the environmental influences that contribute to its onset and advancement. The transition into retirement may be a pivotal moment impacting cognitive functioning. This study aimed to synthesise evidence on the effects of retirement on cognitive functioning through a systematic review of longitudinal studies. A systematic search was conducted in the CINAHL and APA PsycArticles databases, as well as in SciELO, PubMed, Scopus, and Web of Science, for studies published since 2013, following PRISMA guidelines. Twenty-two studies were selected. A narrative synthesis of the main characteristics and results of the included studies enabled the identification of overarching trends as well as confounding and moderating variables in the relationship between retirement and cognitive functioning. Overall, the findings suggested that retirement was associated with lower cognitive functioning, an increased rate of decline, and a higher risk of dementia. Sociodemographic variables, cognitive domains assessed, mental job demands, and occupational groups were found to modify this relationship. Possible mechanisms such as reduced cognitive stimulation, increased stress, and role disengagement are discussed.