The versatile uses and excellent soft tissue distinction afforded by magnetic resonance imaging (MRI) has led to the development of many MR-compatible devices for MRI-guided interventions. This paper presents a fully pneumatic MR-compatible robotic platform designed for neurosurgical interventions. Actuated by nonmagnetic pneumatic piston-cylinders, the robotic platform manipulates a five degree-of-freedom active cannula designed for deep brain interventions. Long lines of tubing connect the cylinders to remotely located pressure sensors and valves, and MRI-compatible optical sensors mounted on the robot provide the robot joint positions. A robust, nonlinear, model-based controller precisely translates and rotates the robot joints, with mean steady-state errors of 0.032 mm and 0.447 deg, respectively. MRI-compatibility testing in a 3-Tesla closed-bore scanner has shown that the robot has no impact on the signal-to-noise ratio, and that geometric distortion remains within recommended calibration limits for the scanner. These results demonstrate that pneumatic actuation is a promising solution for neurosurgical interventions that either require or can benefit from submillimeter precision. Additionally, this paper provides a detailed solution to the control problems imposed by severe nonlinearities in the pneumatic system, which has not previously been discussed in the context of MR-compatible devices.