The Kenyan Constitution of 2010 aimed to improve provision of public health services by mandating counties to offer decentralized services. Counties have continually made reforms to ensure provision of high-quality and effective services. Despite constant reforms, challenges persist in delivering efficient services. Public sector hospitals are struggling to perform well because they haven't fully embraced the WHO‘s recommended good practices due to: poor management, inefficiency, underfunding, inadequate healthcare workers, poor physical facilities, and issues with technology and pharmaceuticals, contributing to substandard services. This study aimed to assess selected HR practices‘ effect on service delivery in the public health sectors of Bungoma and Siaya counties. The objectives were: assess the effect of recruitment and selection practice, determine the effect of leadership style, assess the effect of career development management, establish the effect of employee motivation on service delivery and determine the moderating effect of work environment on the relationship between HR practices and service delivery in the public health sectors of Bungoma and Siaya counties. Resource-based view theory, Hertzberg‘s two factor theory, and agency theory were adopted. Pragmatism philosophy was adopted. A mixed methods research design was used. The target population was 3,549 comprising of healthcare workers, inpatients and HROs from both counties and a sample size of 369 respondents was selected using proportional allocation. Multi- stage sampling approaches were used. Questionnaires and interview guides were used for data collection. Data was analyzed using descriptive and inferential statistics and SPSS. These included: Simple linear regression, Pearson correlation coefficient and multiple linear regression models. The findings indicate that recruitment and selection practice, leadership style, career development management and employee motivation have a significant effect on service delivery with = 0.647, 0.764, 0.876, 0.685 and p= values<0. 05 respectively. Work environment has a moderation effect on the relationship between recruitment and selection practice with ß = 0.0997, p =0.0297 < 0.05, career development management ß = 0.1054, p-value =0.0374 < 0.05 and employee motivation ß = 0.1495, p =0.001 < 0.05 on public health sector service delivery. It did not have significant moderation effect on the relationship between leadership style and public health sector service delivery with ß = - 0.0891, t =0.4999, p =-0.618 > 0.05. The study recommends that counties to: embrace and proficiently implement the selected HR practices, formulate and adopt improved recruitment and selection strategies, invest in training programs for managers and supervisors in the health sector to enhance their capacity for quality supervision, develop comprehensive career progression guidelines to promote fair advancement opportunities for healthcare workers across cadres, formulating enhanced motivation strategies that acknowledge and reward performance thus ensuring fairness in the promotion and training processes for healthcare workers, substantially invest in cultivating a conducive work environment in the public health sector by providing ample facilities to ensure a sustainable work environment.The study purposes to fill the knowledge gap by exploring and analyzing the dynamics of HR practices‘ application and their effect on service delivery within the public health sectors of Bungoma and Siaya counties since the advent of devolution. The following suggestions are made: a comparative study in the private health sector, an inquiry to establish why work environment does not moderate the relationship between leadership style and service delivery and a similar research be conducted in other counties.