Little is known about the association between measured intelligence and how people participate in democratic processes. In the 1970 British Cohort Study, we examined the association between childhood intelligence and, at age 34: whether and how people voted in the 2001 UK general election; how they intended to vote; and whether they had taken part in other political activities. People with higher childhood intelligence were more likely to vote in the 2001 election (38% increased prevalence per SD increase in intelligence), and were more likely to vote for the Green Party and the Liberal Democrats (49% and 47% increased prevalence per SD increase in intelligence, respectively). The intelligence-Green party voting association was largely accounted for by occupational social class, the intelligence-Liberal Democrat voting association was not. Similar associations between intelligence and preference for the Green Party or Liberal Democrats were found as regards voting intentions, but neither of these associations was accounted for by occupational social class. People with higher childhood intelligence were more likely to take part in rallies and demonstrations, and to sign petitions, and expressed a greater interest in politics (40%, 65%, 33%, and 58% increased prevalence per SD increase in intelligence, respectively). (Contains 6 tables.)