Cognitive style constitutes an important component of individuals' life history and defines everyday life. However, inter-individual variations in cognitive styles have not been well understood from an evolutionary functional approach. In three studies, the present research investigates how childhood unpredictability might be associated with deliberate versus intuitive cognitive styles. Study 1 (N = 301) revealed that lower childhood unpredictability was predictive of slower life history strategies, which in turn predicted a higher self-reported preference for deliberate cognitive style. Study 2 (N = 269) assessed deliberate versus intuitive responses by using the Cognitive Reflection Test after experimentally manipulating mortality cues. The results showed that individuals who had higher childhood unpredictability, compared with those who experienced lower childhood unpredictability, displayed fewer deliberate responses in the priming condition but not in the control condition. Study 3 (N = 55) used the same manipulation paradigm and tracked participants' eye movements while completing an information search task. Results indicated that, when exposed to mortality cues, participants with an unpredictable childhood, compared to those with a stable childhood, had fewer fixations, spent less time on information search, and examined fewer pieces of information before making a decision. Together, the three studies suggest that childhood unpredictability might calibrate one's cognitive styles to serve distinct adaptive functions in different ecological conditions. The cognitive styles are manifested both as stable life-history propensities and as situationally activated states in response to mortality cues.