(1) Background: High-Intensity Functional Training (HIFT) is a new exercise modality that emphasizes multi-joint functional movements adaptable to any fitness level and promotes greater muscle recruitment. Previous studies have evaluated the positive effects of HIFT on mental and cognitive health but have not evaluated it in older people. This study aims to conduct a systematic review of randomized controlled trials assessing the effects of HIFT on general cognition in older adults with cognitive impairment. (2) Methods: Following the PRISMA 2020 guideline, articles that did a high-intensity functional physical exercise intervention on cognitive performance in older adults with mild to moderate cognitive impairment (MMSE > 10) or dementia, aged 55 years or older, published between 2011 and 2021 in five different electronic databases: PubMed, Web of Science, Scopus, CINAHL, and Cochrane plus were included. (3) Results: 7 articles were included, all having general cognition as their primary outcome. All assessed general cognition using the Mini-Mental State Examination, the ADAS-Cog, or both. All studies had at least one HIFT experimental group with a frequency of 2 sessions per week and a variable duration between protocols of 12, 13, 16, and 26 weeks. Two articles showed that a progressive HIFT program improves general cognition, four articles showed no significant changes within or between groups and one article concluded that a HIFT intervention does not slow cognitive decline. (4) Conclusions: Evidence exists of the benefits of HIFT on general cognition in older adults with cognitive impairment, assessed using the MMSE, the ADAS-cog, or both. Two articles that showed improvement in cognitive function used progressive HIFT with 80% RM at 6, 12, and 1 weeks; however, in the other articles, due to the heterogeneity of intervention protocols, measurement time points, and control group activities, mixed results were evidenced