The potential energy curves (PECs) of three low-lying electronic states of P ion, X2Πu, A2Σ, and B2Σ, have been studied using the full valence complete active space self-consistent field method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach and MRCI with Davidson correction (+Q). The correlation-consistent basis sets, aug-cc-pV5Z and aug-cc-pV6Z, are used and the total energies are extrapolated to the complete basis set limit. Using these PECs obtained with the MRCI+Q/56-extrapolation, the spectroscopic parameters for these electronic states are determined and compared in detail with experimental data and those of previous studies reported in the literature. The comparison shows that excellent agreement exists between the present results and the available experiments. The first 40 vibrational states for the three electronic states are also computed when the rotational quantum number J equals zero. For each vibrational state, the vibrational level G(υ), inertial rotation constant Bυ, and centrifugal distortion constant Dυ are determined when J = 0, which are in good accord with the available measurements. © 2012 Wiley Periodicals, Inc.