Exhausted olive pomace (EOP) biochar prepared by carbonization at 400 °C is investigated as fuel in direct carbon fuel cell (DCFC) with an electrolyte supported configuration. Feasibility of using EOP biochar in DCFC is confirmed showing a maximum power density of 10 mW.cm-2 at 700 °C. This limited DCFC performance is compared with other biochars prepared under similar conditions and interrelated to variable biochar physico-chemical characteristics and their impact on DCFC chemical and electrochemical reaction mechanisms. High ash content (21.55%) and low volatile matter (40.62%) of EOP biochar are among the main causes of DCFC limited output. Silica is the major impurity in EOP biochar ash explaining the limited cell performance as it causes low reactivity and limited electrical conductivity because of its non-crystal structure. The relatively poor DCFC performance when fueled by EOP biochar can be overcome by further pre- and post-treatment of this renewable fuel.