Biogas-fed solid oxide fuel cell (SOFC) technology based on Ni-GDC electrolyte-supported cell (ESC) offers a sustainable solution for European farms’ heat and power demands with superior efficiency. However, the understanding of the degradation and recovery behavior of the Ni-GDC based ESC under processed biogas environment is limited. This study investigates the responses of various electrochemical processes to the degradation under two cases: (1) cold recirculation before reformer (CB) and hot recirculation before reformer (HB) with no risk of carbon deposition. Chronopotentiometry and current–voltage (IV) results indicated that CB case had the highest degradation rate of -11.6 mV/kh, followed by the HB case with -6.4 mV/kh and the dry H2 case with -0.42 mV/kh. With the electrochemical impedance spectroscopy (EIS) measurements and distribution of relaxation time (DRT) method, it was found that CB and HB case demonstrated much lower gas conversion resistance than the dry H2 case, while two peaks representing the electrode gas diffusion process integrated with O2− surface exchange merged into one peak in HB and dry H2 case but split in CB case. Complex nonlinear least squares (CNLS) fit was used to quantify the resistance degradation under CB and HB environments, which depended mainly on the ohmic resistance and two electrode charge transfer resistances. The recovery process under dry H2 environment showed that the total resistance increased after 134 h, validating the degradation inertia under biogas environment, while the time constants of RQ elements and the peak shifting indicated that the electrochemical performance was partially recovering to the initial state. This study provides insights into the long-term performance degradation of Ni-GDC based ESC under processed biogas environment and guidelines to the operating conditions with a lower degradation rate.