In the title complex, [Mg(C44H28N4)(C6H4N2)(H2O)], the Mg(2+) cation is octa-hedrally coordinated and lies on an inversion center with the axially located 4-cyano-pyridine and aqua ligands exhibiting 50% substitutional disorder. The cyano-bound 4-cyano-pyridine mol-ecule also is disordered across the inversion centre. The four N atoms of the pyrrole rings of the dianionic 5,10,15,20-tetra-phenyl-porphyrin ligand occupy the equatorial sites of the octa-hedron [Mg-N = 2.0552 (10) and 2.0678 (11) Å] and the axial Mg-(N,O) bond length is 2.3798 (12) Å. The crystal packing is stabilized by weak inter-molecular C-H⋯π inter-actions.