The climate affects maize production. Unpredictable rainfall timing, frequency, duration, character, and distribution, particularly during the growing season; rising temperatures exceeding the levels appropriate for maize production; and high incidences of pests and diseases all contribute to declining yields and increased food insecurity. The goal of the study was to find out how much smallholder maize production in Kitui and Laikipia counties was affected by changes in the weather. A questionnaire was used to collect demographic and socioeconomic information from 397 smallholder maize producers. The National Oceanic and Atmospheric Administration provided monthly temperature data in degrees Celsius derived from a combination of Global Historical Climatology Network gridded version 4 and Climate Anomaly Monitoring System datasets. The Centennial Trends version 1.0 precipitation dataset provided monthly rainfall data in millimeters. The vulnerability index was created by combining the exposure, sensitivity, and adaptive capacity indices derived through factor analysis. Drought, famine, climatic changes, crop failure, and purchasing maize increased the vulnerability of smallholder maize production, whereas less frequent water fetching, increased maize yield, access to extension, input subsidies, fertilizer expenditure, and the number of social groups decreased vulnerability. According to the study, smallholder maize production in semi-arid lowland areas was more vulnerable to climate variability than in highland areas. The findings suggest that the national and county governments should monitor vulnerability indicators at the national, county, sub-county, and ward levels in order to inform the design and implementation of appropriate vulnerability-reduction programs.