The aim of this systematic rapid review was to explore barriers, facilitators, perceptions and preferences of physical activity for people diagnosed with cancer, by cancer type and treatment stage. The search strategy, implemented through four databases, included terms relating to cancer, physical activity, barriers, facilitators, perceptions and preferences, and relevant study designs. Studies reporting the outcomes of interests for adults diagnosed with cancer and living in Western countries were included and grouped according to the Social-Ecological Model and the Health Belief Model, and pragmatically. A total of 118 studies, involving 15 cancers were included. Outcomes were most commonly explored within samples involving mixed cancers (32 studies) and breast cancer (31 studies), and at the post-treatment phase (52 studies). Across all cancers and during- and post-treatment, treatment- and disease-related side-effects were the most commonly identified barrier, social support and guidance was the most commonly identified facilitator, and promoting health and recovery was the most commonly identified perception of benefit of physical activity. Notable differences were identified in barriers, facilitators and perceptions across cancer types and treatment stages, with specific examples including: comorbidities were inconsistently reported as a barrier across cancers; time pressure was more commonly reported as a barrier post-treatment; and women with breast cancer reported inaccessibility of appropriate services more commonly during-treatment than post-treatment. Preference findings varied widely across cancer types and treatment phases. These findings can be used to aid efforts to improve physical activity levels post-cancer by providing healthcare professionals with information to facilitate individualised advice and services.