In high-performance sport, an athlete's ability to overcome setbacks and sustain their pursuit of long-term goals is essential for success. Grit (i.e., passion and perseverance over long-terms) has been linked to success in a variety of domains but is often critiqued for its limited predictive utility when compared to other psychological variables including self-control, conscientiousness, and mental toughness. The purpose of this study was to examine whether grit predicted important athlete outcomes (i.e., various measures of sport performance and athlete well-being) beyond other determinants of success. Data from 214 collegiate student-athletes (111 women, 103 men; M = 21.02, SD = 2.26) from Western Canadian universities were analysed. When predicting performance, the addition of the grit subscales (i.e., consistency of interests, perseverance of effort, adaptability to situations) explained an additional 11% of variance (R = 0.37, F[7, 203] = 7.16, p < .001) beyond self-control, conscientiousness, and mental toughness in subjective sport performance perceptions; however, grit did not add unique variance when entered into models predicting athlete goal achievement perceptions or highest level of competition. When predicting well-being, addition of the grit subscales added 18% of unique variance (R = 0.43, F[7, 203] = 21.43, p < .001) beyond other determinants of success in eudaimonic well-being, and 5% (R = 0.17, F[7, 203] = 6.95, p < .001) in satisfaction with sport, but did not add any unique variance to the model predicting mood. The partial support of the predictive utility of grit illustrates the complexity of forecasting success in sport and offers evidence that grit should continue to be studied as a motivational disposition in the domain of sport.