Automating image-guided therapy and registering a medical image to a patient require knowledge of the locations of both the medical image source (e.g., ultrasound) and the surgical tool with respect to a global coordinate system that is known relative to the patient. Also, sturdiness of the medical instrumentations is essential. A novel compact stabilizer-tracker integrated assembly is designed to serve as a holder that can be used to support, manipulate in six degrees-of-freedom, and firmly lock-in-place ultrasound imaging probes and other instruments for use in image-guided surgery as well as to provide the position and orientation of the probe in 3D space with respect to a known reference origin. The stabilizer’s configuration allows a clinician to easily manipulate an ultrasound probe in 3D space, and demonstrate improved sturdiness when locked. A reliable validation technique using forward kinematics was used to evaluate the performance of the holder. Performance tests show that the tracker assembly can acquire the position and orientation of the ultrasound probe with an average displacement accuracy of and roll, pitch, and yaw angular accuracies of , , and , respectively. The improved sturdiness demonstrated by the compact-sized stabilizer and the high accuracy of the tracking mechanism make the integrated holder mechanism well suited for use in image-guided robot-assisted brachytherapy. It is anticipated that this will lead to improvement in accuracy and clinical outcomes for the procedure. The novel tracker can also be used to acquire the positions and orientations of other passive mechanisms of complex designs.