Qualitative research methods are receiving increasing recognition in healthcare-related studies. Nonetheless, the debate among scholars continues regarding validity in qualitative research; that is, whether the tools, processes, and data used are appropriate. Therefore, this study aims to describe the development and content validation of a focus group discussion (FGD) interview guide, which was utilized to explore practices and factors that influence adolescents’ usage of the Nutrition Information Panel (NIP) for food choices. A methodological study was carried out to assess the content validity of the FGD interview guide through a two-stage process (i.e., development and validation). The FGD interview guide for this study was developed by the researchers following five essential steps: identification of research objectives, selection of topics and questions, development of the guide, expert evaluations, and a pilot test. The developed FGD guide was assessed by five content experts representing a range of disciplines, including nutritionists, academicians, a qualitative researcher, and a teacher. A pilot FGD was conducted using a setting and participant criteria similar to those that will be employed in the main study. The content validity index (CVI) value for the developed FGD guide is 0.938. Seven out of 13 questions were modified based on the experts’ recommendations, such as reviewing an item, splitting it into two if necessary, retaining its original syntax if it was already suitable, or adding some new items. Subsequently, the researchers refined the questions’ wording and structure based on the analysis from the pilot FGD. Probes were also added to several questions to elicit in-depth responses from the participants. The final version of the FGD guide consisted of 13 main items and probes. The content validity of the FGD interview guide used in the pilot study was affirmed by a panel of experts; hence, it was deemed to be a valid instrument for measuring adolescents’ use of the NIP in future studies. Further investigation is needed to improve assessments of procedural knowledge and to test the interview guide in other populations.