The Learner Profile (LP) frames International Baccalaureate (IB) learning outcomes across the three programme levels and, as such, plays a key role in measuring the success of the rapidly growing number of IB schools in the Asia-Pacific Region. Our aim was to develop an instrument to measure the IBLP and validate the instrument through a series of psychometric procedures. Results showed solid construct validity and measurement reliability, alongside content validity from our Delphi studies and cross-validation with different samples. Given the growing number of IB schools in the Asia-Pacific, we believe that the development of the IBLP questionnaire (IBLPQ) contributes to the international research community and educators interested in exploring the relationship between student outcomes and the LP. Importantly, given the current absence of systematically designed and tested survey instruments to measure the LP, we expect the IBLPQ will become a key initial resource for a wide range of stakeholders.