High level electronic structure calculations predict the molecular mechanism of H2 elimination in the LiH + NH3 → LiNH2 + H2 reaction. Geometries and energies of stationary points are obtained using second-order perturbation theory (MP2) and coupled cluster CCSD(T) theory with the aug-cc-pVTZ basis set. The reaction proceeds via intermediate molecular LiNH4 complexes, namely HLi-NH3 (reactant side) and LiNH2-H2 (product side). Each reactant contributes one H atom to the product H2.