This study examined the effect of climate variability and cassava output on food security in Nigeria from 1990 to 2020. Both descriptive statistics and hierarchical multiple regression analysis were used to achieve the objectives of the study. Data for the study were gathered from the Food and Agriculture Organization Statistical database (FAOSTAT); World Bank database; Central Bank of Nigeria Statistical Bulletin and Nigeria Meteorological Agency (NIMET). The result from the study showed that rainfall was a major climatic element that affects cassava production output and food security (average value of food production) in Nigeria. The Beta weights in model 1 showed that rainfall (β= 0.372: P<0.1) had a positive effect on average value of food production. Also, the Beta weights of model 2 showed that cassava output (β= 0.412: P<0.05) had a positive effect on average value of food production. The study therefore recommended that since rainfall affects crop production, there should be adequate provision of artificial irrigation facilities in order to boost cassava production in areas with limited amount of rainfall.