As a result of the global economic recession over the past decade, employees have been exposed to constant threats of job insecurity. Despite having conducted extensive research on job insecurity, scholars have paid little attention to the motivational processes underlying employees’ reactions to job insecurity. The purpose of the present study is to examine the relationship between job insecurity, intrinsic motivation, and performance and behavioral outcomes. Drawing on self-determination theory (SDT), we propose a mediated relationship in which job insecurity decreases intrinsic motivation, which, in turn, undermines job performance, organizational citizenship behavior (OCB), and change-oriented OCB. To test our propositions, we collected survey-based data from 152 R&D professionals employed in a South Korean manufacturing company. As predicted, job insecurity was negatively related to intrinsic motivation, which, in turn, had a positive relationship with all three outcomes. Furthermore, job insecurity exerted significant indirect effects on job performance, OCB, and change-oriented OCB through intrinsic motivation. These findings affirm SDT, which posits that motivation, as a key intermediary process, affects employees’ reactions to job stressors.