The present study investigated the relationships between motivation orientation (approach and avoidance motivations) and ideational flexibility and the potential effects of optimism on these associations in a large behavioral sample of 320 healthy young adults. As predicted, the approach motivation-ideational flexibility relationship and the avoidance motivation-ideational flexibility relationship were differentially affected by individual difference measures of dispositional optimism. More specifically, optimism significantly moderated the relationship between avoidance motivation and ideational flexibility, whereas it did not moderate the relationship between approach motivation and ideational flexibility. Detailed analysis revealed that avoidance motivation related positively to ideational flexibility, especially for people with low optimism. Furthermore, in an external validation analysis using data obtained from an independent sample of participants (replication cohort; n = 249), we showed that dispositional optimism can reliably affect the approach motivation-ideational flexibility relationship and the avoidance motivation-ideational flexibility relationship differentially. These findings help resolve the ongoing controversy surrounding the nature of the motivation orientation-creativity nexus and have potential implications for current practice and interventions.