The concept of sport engagement, emerging from the application of major ideas of positive psychology in sport science, has become a valuable conceptual and practical addition to understanding athlete burnout. The present article reports the major results of an attempt to develop a Polish version of the Sport Engagement Scale, a brief metric created to measure athletes' engagement for both research and practical purposes. Study 1, conducted on a sample of Polish athletes (N = 214) supports the original threefactor structure of engagement comprising the dimensions of Vigor, Dedication, and Absorption. A single-factor model also fit the data well, suggesting that calculating a general engagement factor is also justifiable. The internal consistency of the scale, as well as its associations with athletic burnout, competition anxiety, personality traits, declared sport level, and number of hours spent in training, provide evidence for sufficient concurrent criterion validity and the reliability of the scale for both research and applied purposes. Study 2, conducted on a sample of athletes taking part in a half marathon run (N = 135), provides evidence for the scale's predictive criterion validity with respect to objective performance: greater engagement, particularly scores in the Vigor subscale, predicted significantly better running performance. In the discussion, we summarize the present findings, commenting on their limitations and highlighting future research paths for the phenomenon of sport engagement.