Safe and stable immobilization of spent adsorbents is a crucial step in nuclear and radioactive waste management. This study provides the first example of the green immobilization of simulated radioactive cesium-adsorbing MXene (Ti₃C₂T_x) by using hydroxyapatite (HAp) ceramic as a host matrix. The MXene-HAp (MX-HAp) composite exhibited a significantly enhanced thermal stability than that of the pure Cs-adsorbing MXene. The immobilization process was carried out by cold sintering at a low temperature (200 °C), which prevented the possible oxidation and chemical degradation of the spent adsorbent. The developed composite ceramic matrix was highly dense (3 ± 0.01 g·cm⁻³), mechanically strong (microhardness 2.2 ± 0.2 GPa), and chemically stable. The normalized leaching rate of simulated radioactive cesium was calculated to be 2.02 (±0.09) × 10⁻⁴ g·m⁻²·d⁻¹. Thus, the thermal stability of MXene was enhanced using the HAp dried ceramic powder and non-volatile immobilization of the dried MX-HAp composite was achieved by cold sintering. The reported immobilization process showed no adverse effects on the stoichiometry of the composite matrix materials and no volatilization loss of the adsorbed simulated radionuclide was observed. This study is set to take the green immobilization process for spent adsorbents to the next level by combining MXenes and HAp to develop different types of composite materials.