IntroductionPeople with advanced cancer can experience a wide range of multidimensional symptoms or concerns, but little is known about when and how these fluctuate in daily life. Experience sampling methods (ESMs) involve repeated self-reports in people’s natural contexts aimed at uncovering everyday life experiences. ESM has limited recall bias and good ecological validity but might be burdensome to patients. This study aims to pretest and evaluate the feasibility and clinical utility of a validated ESM and use it to explore everyday experiences of people living with advanced breast or lung cancer.Methods and analysisIn step 1, we will optimise our ESM method by pretesting it through usability interviews and a pilot ESM study. In step 2, we will evaluate and use the ESM method through an observational ESM study to investigate the daily experiences of people with advanced breast or lung cancer. Step 2 also includes interviews with healthcare professionals to determine the clinical utility of ESM in oncology. Participants will complete a digital questionnaire ten times per day, measuring momentary experiences in the physical, psychological, social, spiritual-existential domains and context. Multilevel regression models will analyse fluctuations and temporal relations among measured experiences and context. Analyses also include evaluation of compliance and participation rates. We will apply content analysis to the usability interviews and follow-up interviews of the pilot ESM study.Ethics and disseminationWe obtained approval from the ethics committees of the University Hospitals of Brussels (BUN: 1432023000043) and Ghent (ONZ-2023-0136). Results will be published in open-access, peer-reviewed journals and presented at conferences. If ESM appears feasible in this population, it could offer new insights into the daily experiences and help optimise support for people with advanced cancer.