This article examines the influence of leadership style on organizational effectiveness. Research design used was explanatory and descriptive. The population of the study was project managers of 5547 NGOs registered in Kenya in the year 2016. The data collection tool was a questionnaire. The study sample size was 374 project managers from NGOs in Kenya. Data was analyzed using descriptive and inferential statistical methods. The descriptive statistics methods used included mean, standard deviation and variance, while the inferential statistics used in the study included analysis of variance (ANOVA), and standardized coefficients. Leadership style construct is in three parameters: Clear instructions, concern for employees, and employee consultation. The construct parameters of organizational effectiveness are organization goals attainment, stakeholder satisfaction, and process efficiency. The linear regression model results explain 15.1 percent of the variation in organizational effectiveness and the 84.9 percent from error term and variables not examined in this research. The F statistic was 49.875 at P value of 0.000, meaning that the leadership style has a significant influence on organizational effectiveness. Clear instructions significantly and positively influenced the attainment of organizational goals (p=0.001). Concern for employees was found to significantly and positively facilitate the attainment of organizational goals (p=0.009) and significantly and negatively influence stakeholder satisfaction (p=0.006). In addition, concern for employees significantly and negatively influenced organizational process efficiency (p=0.009). The study recommends that leaders in an organization should provide distinct instructions and be concerned about employees to achieve process efficiency and goal attainment.