Background: The leaves of Origanum majorana (O. majorana) are traditionally renowned for treating diarrhea and gut spasms. This study was therefore planned to evaluate its methanolic extract. Methods: Gas chromatography–mass spectrometry (GC-MS) was used to identify the phytochemicals, and Swiss albino mice were used for an in vivo antidiarrheal assay. Isolated rat ileum was used as an ex vivo assay model to study the possible antispasmodic effect and its mechanism(s). Results: The GC-MS analysis of O. majorana detected the presence of 21 compounds, of which alpha-terpineol was a major constituent. In the antidiarrheal experiment, O. majorana showed a substantial inhibitory effect on diarrheal episodes in mice at an oral dosage of 200 mg/kg, resulting in 40% protection. Furthermore, an oral dosage of 400 mg/kg provided even greater protection, with 80% effectiveness. Similarly, loperamide showed 100% protection at oral doses of 10 mg/kg. O. majorana caused complete inhibition of carbachol (CCh, 1 µM) and high K{}^{+} (80 mM)-evoked spasms in isolated ileal tissues by expressing significantly higher potency (p 0.05) against high K{}^{+} compared to CCh, similar to verapamil, a Ca{}^{++} antagonist. The verapamil-like predominant Ca{}^{++} ion inhibitory action of O. majorana was further confirmed in the ileal tissues that were made Ca{}^{++}-free by incubating the tissues in a physiological salt solution having ethylenediaminetetraacetic acid (EDTA) as a chelating agent. The preincubation of O. majorana at increasing concentrations (0.3 and 1 mg/mL) shifted towards the right of the CaCl{}_2-mediated concentration-response curves (CRCs) with suppression of the maximum contraction. Similarly, verapamil also caused non-specific suppression of Ca{}^{++} CRCs towards the right, as expected. Conclusions: Thus, this study conducted an analysis to determine the chemical constituents of the leaf extract of O. majorana and provided a detailed mechanistic basis for the medicinal use of O. majorana in hyperactive gut motility disorders.