In the title compound, C(26)H(23)BrP(+)·Br(-)·C(2)H(3)N, the dihedral angles between the plane of the benzylic phenyl ring attached to the P atom and the planes of the three directly attached phenyl rings are 34.04 (12), 45.48 (13) and 87.18 (9)°. In the crystal, centrosymmetric pairs of cations and anions are linked into dimeric aggregates via C-H⋯Br hydrogen bonds. There is also a C-H⋯N hydrogen bond to the acetonitrile solvent mol-ecule.