Background: In 2020, the World Health Organization (WHO) released global guidelines on physical activity (PA) and sedentary behavior, for the first time providing population-based recommendations for people living with selected chronic conditions. This article briefly presents the guidelines, related processes and evidence, and, importantly, considers how they may be used to support research, practice, and policy. Methods: A brief overview of the scope, agreed methods, selected chronic conditions (adults living with cancer, hypertension, type 2 diabetes, and human immunodeficiency virus), and appraisal of systematic review evidence on PA/sedentary behavior is provided. Methods were consistent with World Health Organization protocols for developing guidelines. Results: Moderate to high certainty evidence (varying by chronic condition and outcome examined) supported that PA can reduce the risk of disease progression or premature mortality and improve physical function and quality of life in adults living with chronic conditions. Direct evidence on sedentary behavior was lacking; however, evidence extrapolated from adult populations was considered applicable, safe, and likely beneficial (low certainty due to indirectness). Conclusions: Clinical and public health professionals and policy makers should promote the World Health Organization 2020 global guidelines and develop and implement services and programs to increase PA and limit sedentary behavior in adults living with chronic conditions.