In this study, a two-degree-of-freedom (2-DOF) wave energy converter (WEC) composed of an eccentric dual-axis ring and power generators using circular Halbach array magnetic disks and iron-core coils was developed. The 2-DOF WEC was designed to convert kinetic energy from the pitching, rolling, and heaving motions of a mooring-less buoy. The eccentric dual-axis ring with appropriate weighting conditions enhanced power generation by revolving in biaxial hula-hoop motion, because it exhibited a higher angular velocity than when in swing motion. Kinetic equations for the biaxial eccentric dual-axis ring mounted on the buoy were derived using the Lagrange Euler equation. Furthermore, weighting conditions of the eccentric dual-axis ring for biaxial hula-hoop motion were determined in accordance with frequency and amplitude of regular buoy motion. The magnetic flux density, cogging torque, and electromagnetic damping of the magnetic disk were evaluated using magnetic field strength simulations and Faraday's law of induction. The 2-DOF WEC prototype was implemented, and biaxial hula-hoop motion was observed in a wave flume test. An output power of 0.56 W was generated for the primary frequency of buoy motion from 0.7 to 1.0 Hz. Results indicate the WEC is feasible as a sustainable power source for sensors on buoys. (C) 2019 Elsevier Ltd. All rights reserved.