INTRODUCTION: Nonagenarians and centenarians, compared with other age groups, often exhibit distinct physiological characteristics and a higher prevalence of comorbidities, thus further complicating their care in intensive care unit (ICU) settings. Despite the increasing number of such patients being admitted to ICUs, comprehensive research and studies on their characteristics, outcomes and complications during their ICU stays remain lacking. This scoping review will comprehensively address the following question: What are the characteristics, outcomes, complications and mortality rates among nonagenarians and centenarians admitted to ICUs, including their preadmission health status, reasons for admission, duration of hospital/ICU stays, and factors associated with adverse outcomes? The key objectives are to map the breadth and depth of the available evidence and identify key concepts, gaps and variations in research focus. Finally, we aim to highlight well-studied areas suitable for systematic synthesis, point to underexplored topics warranting further investigation and propose standardised approaches to research design and reporting in this domain. METHODS AND ANALYSIS: We will conduct a systematic search of MEDLINE, Embase and the Cochrane Library in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews guidelines. All studies and publications reporting data on patients aged ≥90 years will be included, from an unlimited timeline to 31 August 2024. Studies reporting the characteristics, outcomes and complications of nonagenarians and centenarians admitted to ICUs will be included. The data will be analysed and summarised descriptively through a narrative approach. Qualitative data related to quality-of-life outcomes will be analysed thematically, as applicable. ETHICS AND DISSEMINATION: Ethics approval was not required. The findings will be disseminated through professional networks, conference presentations and publications in scientific journals.