For some people, COVID-19 infection leads to negative health impacts that can last into the medium or long term. The long-term sequelae of COVID-19 infection, or 'long COVID', negatively affects not only physical health, but also mental health, cognition or psychological well-being. Complex, integrated interventions are recommended for long COVID, including psychological components; however, the effectiveness of such interventions has yet to be critically evaluated. This protocol describes a systematic review to be conducted of scientific literature reporting on clinical trials of interventions to promote mental health, cognition or psychological well-being among individuals with long COVID. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines will be followed. A health sciences librarian will identify the relevant literature through comprehensive systematic searches of Medline, Embase, APA PsycINFO, Cumulative Index to Nursing and Allied Health Literature, medRxiv, PsyArXiv, China National Knowledge Internet and WANFANG Data databases, as well as The Cochrane Central Register of Controlled Trials, clinicaltrials.gov and the WHO International Clinical Trials Registry Platform. Studies will be selected through a title and abstract review, followed by a full-text review using inclusion and exclusion criteria. Data extracted will include intervention descriptions and efficacy metrics. Data will be narratively synthesised; if the data allow, a meta-analysis will be conducted. Risk of bias assessment will be conducted using the Cochrane Risk of Bias 2.0 tool. Ethical approval for systematic reviews is not required. As researchers and clinicians respond to the new clinical entity that long COVID represents, this review will synthesise a rapidly emerging evidence base describing and testing interventions to promote mental health, cognition or psychological well-being. Results will therefore be disseminated through an open-access peer-reviewed publication and conference presentations to inform research and clinical practice. CRD42022318678. [Abstract copyright: © Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.]