Over the past few decades, media and technology use have become increasingly significant components of everyday life. Given media's ubiquitous usage across the lifespan, it is important to understand what puts individuals at risk for engaging in problematic media use. Thus, the current study aimed to explore youth affective-behavioral vulnerability and peer processes as predictors of excessive and problematic media use in young adulthood. Specifically, anxious solitude and peer exclusion trajectory classes in elementary school (3rd to 5th grade) were explored as predictors of young adult media behaviors. Further, membership in anxious solitude and peer exclusion trajectory classes in middle school (6th to 7th grade) were tested as explanatory processes (mediators) in the link between elementary school trajectory class membership and young adult media use. For the trajectory class analysis, participants were 688 youths who had taken part in the Multiple Trajectories in Anxious Solitary Youth study (female n = 354; 51.5%). Latent class growth analysis (LCGA) was used to identify trajectories of peer-reported peer exclusion in childhood (trajectories of peer-reported anxious solitude with this data have been identified in the extant literature; Gazelle & Faldowski, 2019). Separate analyses were conducted for elementary and middle school to allow for different trajectory patterns to emerge after the middle school transition. Three peer exclusion trajectory classes were identified in elementary school (low-stable, moderate-stable, and high-increasing) and two in middle school (low-stable and high-increasing) with latent class growth analyses (LCGA). In Gazelle and Faldowski's (2019) study, two anxious solitude trajectory classes were identified in elementary school (moderate-decreasing and high-increasing) and three in middle school (low-stable, low-increasing, and high-decreasing). For the main analysis, participants were 118 young adults (female n = 76; 64%; M age at survey completion = 22.8 years, SD = 0.84) who had been prospectively assessed from 3rd to 7th grade in the Multiple Trajectories in Anxious Solitary Youth study. Structural equation modeling (SEM) was used to investigate the influence of anxious solitude and peer exclusion trajectory class membership (in elementary school) on excessive and problematic media use in young adulthood. Further, middle school trajectory classes (both anxious solitude and peer exclusion) were tested as mediators of this link. In partial support of the direct effect hypotheses, membership in the elementary school high-increasing anxious solitude trajectory class and high-increasing peer exclusion trajectory class predicted more hours per day spent playing video games in young adulthood. Additionally, elementary school moderate-stable peer exclusion trajectory class membership predicted more time spent using social media and the internet for entertainment in young adulthood. Finally, although the mediation hypothesis was not supported, mediation analyses revealed that middle school low-increasing anxious solitude trajectory class membership fully mediated the link between elementary school high-increasing anxious solitude trajectory class membership and more time playing video games in young adulthood. Further, middle school high-increasing peer exclusion trajectory class membership partially mediated the link between elementary school high-increasing peer exclusion trajectory class and less time using social media in young adulthood. This study suggests that young adults with a history of anxious solitude or peer exclusion in elementary school may be especially vulnerable to excessive media use as young adults. Further, this study highlights how continuity and different developmental pathways of anxious solitude and peer exclusion may explain why some anxious solitary and excluded youths spend more (or less) time using media than their anxious solitary and excluded counterparts. Limitations, future research directions, and implications of the study are discussed.