Background: This study aimed to describe the levels of physical activity (PA) in adults living with and beyond cancer (LWBC), using self-report and pedometer data, and to describe associations with well-being. Methods: Data were from baseline assessments in the ‘ASCOT’ trial (1348 breast, prostate or colorectal cancer patients recruited 2015-2019). A modified Godin-Shephard Leisure Time PA Questionnaire was used to calculate the Leisure Score Index (LSI, ≥24 considered active) and weekly minutes of Moderate-Vigorous PA (MVPA, 150 considered active). Pedometer data was used to calculate daily step count (8000 considered active for older adults). Loneliness (UCLA loneliness scale), fatigue (FACIT-Fatigue), quality of life (EQ-5D descriptive scale), sleep quality (PSQI) were measured. Multiple imputation was used to account for missing data. Multiple linear regressions were conducted to examine associations between these variables and each of the PA outcomes, controlling for clinical and demographic variables. Findings: 621/1254 (50%) were classified as active on the LSI, 548/1235 (44%) using MVPA and 284/1236 (23%) on mean daily steps. Lower fatigue was associated with higher levels of PA across all outcomes (LSI (β = 0.111, p = 0.003) MVPA (β = 0.123, p = 0.001), daily step count (β = 0.162, p < 0.001)). Higher quality of life was associated with higher daily step count (β = 0.108; p = 0.005). Discussion: There is a need to promote PA in those LWBC, and this is more evident when an objective measure is used. Different conclusions may be drawn when different measures of PA are used.