Although the concept of employee sustainable performance has received considerable attention in the practitioner literature, academic research still lacks a clear conceptualization and empirical operationalization of this concept. Defining employee sustainable performance as a regulatory process in which an individual worker enduringly and efficiently achieves particular desired work goals while maintaining a satisfactory level of well-being, this paper describes a corresponding instrument called E-SuPer, and examines its psychometric properties. The E-SuPer instrument was tested and cross-validated using two cross-sectional survey studies (n = 153 and n = 160), focusing on factorial validity, internal consistency, and discriminant and concurrent validity. Psychometric findings across the two samples revealed that the E-SuPer instrument consists of one general factor of ten items with good internal consistency. Discriminant validity and concurrent validity with other relevant constructs (task performance, counterproductive work behavior, and employee vitality) were also confirmed, showing promising results. Finally, theoretical and practical implications, as well as suggestions for future research, are outlined.