Retirement from competitive sports significantly influences former athletes’ well-being. We propose that disengaging from the former athletic career is a crucial factor in retired athletes’ adaptation. Using the theoretical framework of Self-Determination Theory (SDT) we propose that sport motivation at the career peak and motivation for retirement are important determinants of athletes’ disengagement progress from a terminated athletic career. We also seek to examine how motivation for retirement and disengagement progress predict retired athletes’ well-being. Using a mixed-retrospective/prospective longitudinal design we followed 158 government-supported elite athletes who had recently retired from an athletic career. In two online surveys administered 1.5 years apart, retired athletes reported on motivation, disengagement, and well-being. Results suggested that SDT motivation factors are important predictors for elite athletes career disengagement and well-being in retirement. The clinical implications of these findings for athletic career transition and support programs are discussed.