Objective To construct a comprehensive model of predictors of IQ and its developmental trajectories in survivors of very preterm birth from childhood to adult life. Methods We examined trajectories of Full-scale, Verbal and Performance IQ from age 8 to 30 years in individuals who were born very preterm (textless33 weeks of gestation). Using linear mixed-effect modelling and model selection procedures, we systematically evaluated the impact of perinatal and socio-demographic factors on all IQ subtypes and their trajectories. Results The association between all IQ subtypes and gestational age, socio-economic status and sex was stable over the studied time points. There was a linear association between IQ and gestation age when considering the full gestational age spectrum, following removal of participants born at 24 weeks of gestation. For those individuals born between 25 and 33 weeks, every full gestational week was associated with 1.4 points increase in Full-scale IQ (95% confidence interval (CI): 0.64–2.15) and 1.3 points increase in IQ subtypes (95% CI: 0.64–2.01). Younger gestational age was associated with lower Performance IQ to a greater extent than Verbal IQ. Low SES was associated with lower Full-scale IQ and males had higher Full-scale IQ than females. Conclusion Individuals who were born very preterm, and especially those born at the lower end of the gestational age spectrum, continue to be at higher risk of cognitive impairment in adult life, with their Performance IQ being particularly affected.