INTRODUCTION: Adults with intellectual disability (ID) have lower physical fitness levels than their peers without disabilities, representing a risk to their health since physical activity and cardiorespiratory fitness are directly related to better health and quality of life. Therefore, it is essential to determine the effects that exercise can have on them, as adults with ID present high comorbidities and lower life expectancy, altogether with lower rates of physical activity. The current overview of systematic reviews aims to provide an outline of the exercise benefits in health-related and skill-related fitness in adults with ID. METHODS AND ANALYSIS: Research will be conducted in PubMed, CENTRAL, EMBASE, PEDro, SPORTDiscus and CINAHL. The search terms will be categorised through population (eg, adult, ID); intervention (eg, exercise, physical activity) and outcomes (eg, cardiorespiratory fitness, body composition, muscular strength, muscular endurance, flexibility, balance, power, speed, agility, coordination, mobility and reaction time). Each database will be searched from their earliest available record up to 30 September 2021.Inclusion criteria will be: systematic reviews including at least one RCT that compare exercise interventions with a control group or another type of intervention; measure of fitness using objectives methods; inclusion of adults with ID (≥18 years old), and published in any language, with at least their abstract in English, Spanish, French and/or Portuguese. ETHICS AND DISSEMINATION: To our knowledge, our overview will be the first of its kind to address the topic in people with ID. The results could be used to determine which fitness components can be improved by exercise and to provide a valuable tool to develop comprehensive exercise programmes specific to people with ID. Ethical approval is not required. The knowledge generated will be disseminated electronically and in print and presented at conferences. PROSPERO REGISTRATION NUMBER: CRD42021237580.