Many-particle entanglement can be found in the ground state of natural solids and strongly interacting atomic and molecular gases, but it is still experimentally challenging to generate highly entangled states between weakly interacting particles in a scalable way. We describe a one-step method to generate entanglement between polar molecules in the absence of DC electric fields. For molecules in an optical lattice with site separation of a few micrometers, maximally entangled bipartite states can be created using strong off-resonant pulses that are routinely used in molecular alignment experiments. We show that alignment-mediated entanglement in a molecular array is long-lived and discuss applications for quantum information processing and quantum metrology.