Aim: The implantation of the fertilized ovum outside the normal uterine cavity is termed an ectopic pregnancy (EP). Progesterone an important hormone in the regulation and maintenance of pregnancy has been studied with limited validation as a biomarker of this condition. The aim of this study was to determine whether a measurement of progesterone could discriminate an EP from a normal pregnancy. Materials and methods: Serum levels of progesterone were measured by direct chemiluminescence in 140 women with EP and 140 women with normal pregnancy at Sri Ramachandra Medical College and Research Institute, Chennai, India. Statistical analyses were performed using SPSS software version 16.0, and a p value of less than 0.05 was considered significant. Results: The mean progesterone level in EP was 6.4 ng/mL. This was significantly lower than the value of 24.6 ng/mL in normal pregnancy. Receiver operating characteristic (ROC) curve analysis revealed that at a cutoff of 16.22 ng/mL, progesterone was able to distinguish an EP from a normal pregnancy with a sensitivity of 98.6% and specificity of 87.1%. Conclusion and clinical significance: Progesterone measurement in women in early pregnancy can be used to rule out an EP. Especially in the time window of 4–6 weeks of gestation where ultrasonography is inconclusive, we have to rely on biomarkers like progesterone to resolve the treatment modalities at the earliest.