Background: Physical activity (PA) constitutes an effective strategy for the prevention and management of non-communicable diseases (NCDs). Research demonstrates that a substantial proportion of the adult population in Germany does not reach the recommendations for PA. Health literacy (HL) is significantly associated with health behaviours, including PA levels, and various health outcomes. However, no measurement instrument currently exists that assesses HL within the PA context whilst focusing on information processing competences. Therefore, this research aims to integrate HL and PA concepts and to develop a novel measurement instrument for physical activity-related HL (PA-HL) in Germany emphasising information processing competences. Methods: The development and evaluation process employs a mixed-methods design. The instrument development follows a three-phase methodology: First, the conceptualization of PA-HL is defined, including its dimensions and information processing competences with PA focus. Second, during scale development, content and face validity of items are tested through a three-round eDelphi process with experts in HL and PA fields, and cognitive interviews with adults. Third, the novel instrument undergoes psychometric testing in a cross-sectional pilot study utilising principal component analysis and confirmatory factor analysis. Discussion: Through utilising health information on PA, individuals should be enabled to influence their own PA behaviour and that of others to maintain and promote health. The novel PA-HL measurement instrument could be employed in future research and practice to identify the population support needs and difficulties in processing health information on PA. This should facilitate the development and evaluation of public health interventions tailored to the specific needs of population group requirements.