Although conspiracy belief may arise from a frustration of psychological needs, research has yet to investigate these relationships over time. Using four annual waves of longitudinal panel data in New Zealand (2019–2022; N = 55,269), we examined the relationship between four psychological needs (namely belonging, control, meaning in life, and self-esteem) and conspiracy belief. Results from four random-intercept cross-lagged panel models reveal stable between-person effects indicating that those whose core needs are less satisfied tend to exhibit higher levels of conspiracy belief across time. Within-person analyses further identify small cross-lagged effects within individuals: decreases in levels of control and belonging, as well as increases in levels of meaning in life, temporally precede increases in conspiracy belief. Within-person fluctuations in conspiracy belief also have negative cross-lagged associations with control (but not with the three other needs). These data provide novel insights into the psychological factors that foster conspiracy belief.