Following the landmark 2016 U.S. Supreme Court decision in Montgomery v. Louisiana, approximately 2,500 men and women sentenced to mandatory life without the possibility of parole as children (sometimes referred to as “juvenile lifers”) became eligible to be released. As these juvenile lifers re-enter into society, it is important to study their life histories and the consequences of long-term incarceration. Although there have been studies that shed light on prison life and reentry, there is insufficient research using a developmental and life-course perspective to understand the prison life experiences of those confined over the course of their adult lives, and how these experiences shape reentry processes. Specific to adults serving life-sentences, the consequences of long-term incarceration can adversely affect health, education, employment history, and family ties, with consequences for the reentry process. However, given that juvenile lifers begin their incarceration at a key developmental stage, it is unclear how the effects of long-term confinement impacts their maturation process, development, and ultimately, their reentry successes or failures following their release from prison. This concurrent mixed-method study employs both semi-structured life history interviews and life history calendars to examine the effects of the criminal justice system over one’s life course. The study captures the lived experiences of men and women in Pennsylvania before, during, and after serving a mandatory life sentence without the possibility of parole. This study aims to better understand how long-term confinement, which commenced during the critical developmental period of adolescence, shapes human development and reentry processes as well as how children sentenced to life without parole make sense and order their lives and regain normalcy upon release. Findings reveal that long-term imprisonment disordered the normal stages of human development for juvenile lifers and had adverse consequences for other life domains such as health (both physical and mental), educational attainment, employment opportunities, and the ability to sustain meaningful familial and romantic relationships. Findings also suggest that although the prison environment was not conducive to the development of responsible and mature behavior, juvenile lifers still experienced a series of psychosocial transitions. These psychosocial transitions generally unfolded in various stages, which allowed juvenile lifers to maturely cope to the demands of prison life and achieve significant changes and growth over their life course even before the landmark Miller and Montgomery Supreme Court decisions. The discussion of the research findings highlights the importance of understanding the dynamic changes that occur for those who experience long periods of incarceration to provide insight into post-release outcomes. / Criminal Justice