Parathyroid carcinoma (PC) is a rare endocrine malignancy with a poor prognosis. Preoperative diagnosis remains a major challenge in clinical practice because of limited diagnostic methods and non-specific clinical features. This study aimed to describe the distinct plasma metabolic profiles of PC and parathyroid adenoma (PA) patients and identify promising biomarkers for the preoperative differential diagnosis of PC. A total of 115 patients were enrolled in this retrospective study, including 70 patients (24 PC and 46 PA) in the discovery cohort and 45 patients (15 PC and 30 PA) in the validation cohort. Plasma samples were collected before operation. LC-MS/MS analysis was utilised on the discovery cohort to explore the metabolic profile and find out differentially abundant metabolites. Subsequently, potential diagnostic biomarkers were verified in an external validation cohort to find out novel biomarkers for the differential diagnosis of PC before surgery. Compared with the plasma samples of PA patients, a total of three upregulated and 42 downregulated metabolites were identified by MS/MS in the plasma samples of PC patients. The differentially abundant metabolites were significantly enriched in the arachidonic acid, tryptophan, and hormone metabolism pathways. Notably, 7-ketodeoxycholic acid (P = 0.002, AUC = 0.804) and tryptophan (P < 0.001, AUC = 0.838) were confirmed to show high accuracy in differential diagnosis in the validation cohort. Therefore, metabolomics analysis of parathyroid neoplasms revealed significant differences in metabolic profiles between PAs and PCs. The plasma levels of 7-ketodeoxycholic acid and tryptophan could serve as potential diagnostic biomarkers for PC.