People who feel powerless are motivated to gain power, which may include men endorsing hostile sexism to affirm societal power or women endorsing benevolent sexism to affirm power in relationships. We used four waves of an annual longitudinal panel sample (N = 58,405) to test whether within‐person changes in powerlessness predicted subsequent changes in men's hostile sexism and women's benevolent sexism. Results from a random intercept cross‐lagged panel model indicated that men who generally felt more powerless tended to endorse hostile sexism, but within‐person tests did not provide directional evidence linking men's powerlessness with hostile sexism. By contrast, women who generally felt more powerless endorsed benevolent sexism more strongly, and small within‐person lagged effects indicated that upward deviations in women's powerlessness in 1 year predicted stronger endorsement of benevolent sexism the following year. These results provide novel evidence that powerlessness motivates women's benevolent sexism and their toleration of gender inequalities.