The study emulated a randomized controlled trial using data from a prospective cohort of 11,169 Australian women born 1946–1951, collected every 3 years from 1996 to 2019. It compared patterns of moderate-to-vigorous physical activity (MVPA) over 15 years (2001–2016) aged 50–65 years with all-cause mortality causes, cardiovascular disease (CVD) and cancer. Consistent adherence to WHO recommendations (at least 150 minutes of MVPA per week) over the entire period had a protective effect on all-cause mortality versus nonadherence (hazard ratio RR: 0.50, 99.5% CI [0.27, 0.94]; hazard difference RD: −5.2%; Bayes factor BF=5.71). For CVD mortality (RR: 0.50, 99.5% CI [0.19, 1.30]; RD: −2.1%; BF=2.05) and cancer (RR: 0.35, 99.5% CI [0.55, 1.17]; RD: −3.3%; BF=2.26), the findings were less conclusive. Starting to follow the recommendations at age 55, 60, or 65 years had no clear benefit on mortality. Analyzes were adjusted for sociodemographic and health factors using marginal structural models. Limitations include self-reported physical activity and limited generalizability to all middle-aged Australian women. The conclusion recommends that women adhere to physical activity recommendations during midlife for mortality benefits.