This thesis presents the development of an Earth's Field nuclear magnetic resonance multiphase flow meter. This includes establishing the techniques and apparatus necessary to measure multiphase fractions and flowrates via nuclear magnetic resonance. The flow meter has been tested across a wide range of flow conditions, lncluding single-phase flows, two-phase gas/liquid flows and two-phase oil/water flows. The work has utilised advanced interpretation techniques to capture multiphase flow behaviour in flow regimes such as gas/liquid slug flow and oil/water emulsions. Experimental measurements have validated the accuracy of the flow meter as well as robust performance across the flow conditions tested.