A novel magnetic Co-doped MoO2 @C was prepared by in-situ co-pyrolysis and used for catalyzing hydrodeoxygenation (HDO) of bio-derived guaiacol to arenes or substituted phenols controlled by solvent type. Considering the variation of product distributions from the HDO of guaiacol using different solvents, the reaction intermediates of each stage were traced to explore its HDO pathways over Co-MoO2@C. The results show that guaiacol conversion to catechol via specific demethylation instead of direct demethoxygenation induces the entire reactions. Subsequently, catechol was converted to arenes or phenols by selective dehydroxylation or alkylation over Co-MoO2@C using different solvents. The synergy among Co, MoO2, and biochar plays a crucial role in activating H-2 and ethanol, which is the key to achieving high reactant conversion and product selectivities under relatively lower initial H-2 pressure (0.8 MPa). This solvent-controlled trend is also applicable to the catalytic HDO of the ethanol-soluble portion from bagasse. Furthermore, possible mechanisms for bimetallic synergic catalysis of the formation and transfer of active hydrogen atoms were proposed.