ObjectiveEvidence suggests that people with severe mental illness (PwSMI) are 2.1 times more likely to die from cancer before the age of 75, compared to people without Severe mental illness (SMI). Yet, cancer screening uptake is low among PwSMI. This mixed‐methods systematic review aimed to identify the barriers and facilitators for PwSMI deciding to access and attend primary cancer screening of the cervix, breast and colon.MethodsSix electronic databases and two grey literature sources were searched, with 1017 records screened against inclusion criteria. Included papers were appraised and data synthesised using the constructs of Normalisation Process Theory.ResultsTwenty papers met the inclusion criteria. Factors that impact upon uptake of PwSMI accessing cancer screening were found to include age, gender, race, and income. Common barriers to attending screening included poor communication from healthcare staff, stigmatising attitudes, and accessibility problems such as no access to transportation. While, facilitators included social support from friends, family, and healthcare providers.ConclusionsDue to ease and privacy, colorectal screening was found to have fewer barriers when compared to cervical and breast screening. The review identified multiple barriers that can be addressed and targeted to support decision‐making for cancer screening among PwSMI. The protocol was registered with PROSPERO (CRD42022331781).