This work presents a detailed study of the electrochemical performance of a polyphosphazene based gel polymer electrolyte in a lithium metal polymer cell. The polyphosphazene MEEP was chosen because of its favorable properties, such as good thermal and electrochemical stability versus lithium metal. In combination with a liquid electrolyte, consisting of 0.7 mol L−1 LiBOB in EC/DMC, a high ionic conductivity of ∼9·10−4 S cm−1 at 30 °C was achieved. The electrochemical stability window ranges between 0 V and 4.4 V vs. Li/Li+ reference electrode. The gel polymer was drop coated onto the electrode materials and cross-linked to achieve high mechanical stability. The gel polymer showed a very good interface stability at lithium metal electrodes in the prepared full cells, where a stable SEI was formed during initial contact. The full cell tests delivered a stable cycling behavior with more than 1300 cycles and capacities higher than 110 mAh g−1 at high discharge rates of 2CD, without any indication for short circuits caused by lithium dendrites.