We report results of first-principles calculation of novel NpTM2 (Np = naphthalene; TM = V, Mn, Ti, Nb) sandwich nanowires. Most importantly, we find that the magnetic ordering in the NpV2 nanowire can be adjusted by changing its charge state. Its intrinsic antiferromagnetic ordering can be switched to ferromagnetic ordering by injecting electrons, whereas injecting holes to the nanowire can further stabilize the antiferromagnetic state. This carrier-tunable magnetic ordering appears to be unique to the NpV2 nanowire. Moreover, we find that the bonding between the two nearest-neighbor metal atoms plays a key role in controlling the magnetic coupling of charge-neutral NpTM2 nanowires. We predict that the NpMn2 nanowire is ferromagnetic while the NpTi2 and NpNb2 nanowires are antiferromagnetic.