Purpose: School performance is a global issue. There is a great need for the quality education all over the world. To achieve this, school leadership and teachers’ performance have been put to focus. In this quintessence, the study aimed at establishing the influence of the transformational leadership on the teachers’ performance in public county schools in Nyandarua County. Methodology: The study used both qualitative and quantitative research approaches. The cross-sectional survey and the phenomenology design were used to collect the data. Stratified, simple random sampling was employed to select the schools while stratified and systematic random was used to select the teachers and the students. Academic deans, the principals of selected schools and Education County Director were automatically included. Data was collected using questionnaires, document analysis guide and interview guide. Qualitative and quantitative data were concurrently collected and analysed. Descriptive (frequencies, percentage, mean and standard deviation) and inferential statistics (independent t-test, ANOVA) methods were used to analyse the quantitative data. Findings: The study upheld the non-maleficence, benefice and truthfulness as the research ethics requires. The study found that principal scored lowest in individualised consideration. The study concluded that teachers’ performance was important for the school perfomance and principals play key roles in the enhancement of teachers’ performance especially through challenging teachers by their actions. Unique contribution to the theory, practice and policy: The study recommended that principals should challenge teachers with their performance. The county should have induction training at school level for the newly emplored teachers.