Background: Lung Cancer (LC) and particularly non-small cell lung cancer (NSCLC) is considered one of the most lethal types of cancer to date. Suitability and toxicity of treatment, or eligibility of LC patients for clinical trials usually rely on subjective indicators of Performance Status (PS) such as the Eastern Cooperative Oncology Group (ECOG) and Karnofsky indexes. In recent years, however, the use of electronic wearable devices has increasingly come to the fore with the aim of increasing objectivity of PS assessments. These devices are capable of objectively and passively monitor health-related outcomes such as daily physical activity and sleep patterns. Consequently, a comprehensive review of the current state of the art in this matter can provide further insights for future research within oncology areas in general, and lung cancer, in particular. The main goal of this scoping review is to identify and categorize scientific publications that, over the past 10 years, used wearable devices as means of monitoring activity level of LC patients. Methods: The study follows the PRISMA-ScR framework (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews). Results: A total of 32 studies were identified as suitable to be included in the review where (n = 22; 68.7%) focused on physical activity and (n = 10; 31%) in sleep or circadian patterns. Approximately half of the studies used a wrist wearable. Device output included step counts, activity counts, metabolic equivalents, time active, time spent in moderate-to-vigorous activity, sedentary time, sleep duration, sleep efficiency, total sleep time/sleep duration, sleep onset latency, wake times, and wrist movement per minute. However, step counts arose as one of the most representative outcomes of physical activity (n = 17; 53%). In general, higher levels of physical activity and circadian organization (day/night activity balance) as measured by actigraphy, are associated with less fatigue, pain, and better quality of life. Conclusions: This review shows that wearable devices, and especially wrist wearables, are increasingly used in oncology settings as a reliable method to monitor physical and sleep activity and to complement PS assessment. Further research is needed, however, to determine the extent to which this methodology can be used to more directly objectivize current PS assessment itself.