Disordered eating behavior has been linked to suboptimal weight outcomes following metabolic and bariatric surgery (MBS), thereby threatening the most efficacious treatment for severe obesity. While up to 40% of patients may experience loss of control (LOC) eating following MBS, mechanisms driving this behavior are not fully understood. Preliminary evidence suggests that high levels of negative affect (NA) in the moment prompt LOC eating post-MBS; however, it remains unclear whether this momentary relationship is stable or changes over the first several years following surgery. Consequently, this study examined differences in the prospective relationship between NA and LOC eating severity over time post-MBS using three waves of ecological momentary assessment data collection. Participants (n = 143, 87% female), were asked to rate momentary levels of NA and LOC eating severity on their smartphone ≥5 times/day for 7 days at 1-, 2-, and 3-years post-MBS. Both NA and LOC eating were rated on a 1-5 Likert scale, with higher scores indicating more severe symptoms. NA was within- and between-person centered and used as a prospective predictor of LOC eating severity. Analyses evaluated if time post-MBS moderated the relationship. A generalized linear mixed model demonstrated that higher NA predicted more severe LOC eating at the next signal when centered within- and between-subjects. Time post-MBS moderated the within-NA to LOC eating severity effect, such that the relationship remained unchanged between years 1 and 2, but strengthened between years 2 and 3. Findings suggest that momentary NA becomes a more powerful predictor of LOC eating severity as time passes post-MBS, which has important implications for interventions aimed at reducing LOC eating and promoting optimal weight outcomes in the post-surgical period.