The aim of the present study is to validate the Self-Efficacy in Palliative Care Scale (SEPC) in Spanish nursing professionals and students, to describe their levels of self-efficacy, and to determine the influencing factors. A validation study and a cross-sectional descriptive study were carried out, with the data analysed using contrast tests and multiple linear regression; 552 nurses and 440 nursing students participated. The Spanish version consists of 23 items and has a high degree of reliability (α = 0.944). Confirmatory factor analysis revealed one additional factor (i.e., management of psychosocial and spiritual aspects) in comparison to the original scale. Contrast tests revealed that the mean SEPC score was higher in professionals than in students (p < 0.001) and that the professionals who had higher levels of self-efficacy were older (p < 0.001), had more previous training (p < 0.001), and had more experience in end-of-life care (p = 0.001). The linear analysis results confirm a significant association between age and previous training in end-of-life care. The Spanish version of the SEPC is a reliable tool for both nursing professionals and students. The level of self-efficacy of both groups is moderate and is influenced by age, experience, and training in end-of-life care.