In high-dose-rate (HDR) interstitial gynecologic brachytherapy, needles are positioned into the tumor and surrounding area through a template to deliver radiotherapy. Optimal dose and avoidance of nearby organs requires precise needle placement; however, there is currently no standard method for intra-operative needle visualization or guidance. We have developed and validated a 360° three-dimensional (3D) transvaginal ultrasound (TVUS) system and created a sonolucent vaginal cylinder that is compatible with the current template to accommodate a conventional side-fire ultrasound probe. This probe is rotated inside the hollow sonolucent cylinder to generate a 3D image. We propose the use of this device for intra-operative verification of brachytherapy needle locations. In a feasibility study, the first ever 360° 3D TVUS image of a gynecologic brachytherapy patient was acquired and the image allowed key features, including bladder, rectum, vaginal wall, and bowel, to be visualized with needles clearly identifiable. Three patients were then imaged following needle insertion (28 needles total) and positions of the needles in the 3D TVUS image were compared to the clinical x-ray computed tomography (CT) image, yielding a mean trajectory difference of 1.67 ± 0.75°. The first and last visible points on each needle were selected in each modality and compared; the point pair with the larger distance was selected as the maximum difference in needle position with a mean maximum difference of 2.33 ± 0.78 mm. This study demonstrates that 360° 3D TVUS may be a feasible approach for intra-operative needle localization during HDR interstitial brachytherapy of gynecologic malignancies.