The performance of every organization is determined by its ability to manage organizational resources, and among these resources, human resources are considered the key to the performance of the organization. The efficiency with which an organization can perform will depend to a large extent on how its human resources can be managed and utilized. That is why this study focuses on the impact of career development on employee performance in Nigeria's civil service, a study of Ebonyi State Civil Service, South East Nigeria. Using qualitative and quantitative research approaches, a sample of 382 respondents comprising 36 senior management staff, 91 heads of department and supervisors and 265 operational staff was drawn from 3009 employees of the State Civil Service. A purposive sampling technique was used to reach the respondents. Both primary and secondary sources of data were utilized. Questionnaires and in-depth interviews were the instruments for primary data collection and articles from journals, government gazettes and documents formed the secondary sources. Data was presented and analysed with the aid of Statistical Packages for Social Sciences (SPSS) version 21 and Microsoft Excel. The hypothesis was tested using Chi -Square inferential statistics. Findings indicate that there is a significant relationship between career development and employees' job performance, that career development has moderately impacted employee behavioural competencies (attitude to work) in the Ebonyi State Civil Service within the period under review and that insufficient funding and poor salary packages have affected career development and employee performance in Ebonyi State Civil Service, from 2015-2022. Key recommendations include that Ebonyi State Civil Service Commission should prioritize and enhance career development opportunities within the civil service to enable the employees to benefit from and utilize them to maintain positive work attitudes and boost overall organizational performance, that Ebonyi State Civil Service should provide adequate, transparent and fair promotion opportunities based on merit and performance and that Ebonyi State Civil Service should explore alternative funding sources, seek partnerships or grants, and prioritize budget allocations for employee training and resources.