Promoting incidental physical activity (IPA) can help reduce sedentary lifestyles and physical inactivity levels in the population. However, there is heterogeneity in the definition of IPA, and studies have yet to synthesize the empirical findings on this topic. This review aimed to (1) Synthesize the definitions of the IPA used in the scientific literature, (2) Identify the behaviors part of the IPA, and (3) Synthesize the main findings on IPA. The review followed PRISMA guidelines. A systematic search was performed in July 2023, and an update was made in February 2024 in the CINAHL databases by EBSCOhost, Cochrane Library, Pubmed, ScienceDirect, Scopus, and Web of Science. The search phrase was (“incidental physical activity” OR “incidental physical activity of daily living” OR “incidental movement” OR “vigorous intermittent lifestyle physical activity” OR “VILPA” OR “physical activity of daily living”). Fifty-five studies were included, with non-experimental (40), experimental (12), qualitative studies (2), and mixed design (1). Ten different terms for IPA were identified, and a conceptual definition was included in 33 articles. Behaviors measured as part of the IPA were reported in 41 articles. These definitions describe unstructured, unplanned, and unintentional physical activities of daily living that are performed as a by-product of an activity with a different primary purpose during free or occupational time and without specific fitness, sport, or recreation goals. Include light and vigorous intensities ranging from short sessions of < 1 min to prolonged ones. They include home activities, self-care, gardening, occupation, active transportation, and walking. Furthermore, evidence on IPA suggests an association with a lower risk of all-cause mortality. The findings of this review contribute to the updated study of IPA. Advances in data processing methods are needed to capture the diversity of behaviors and deepen the understanding of IPA.