Two-dimensional (2D) magnetoelectric multiferroic materials with the coexistence of magnetization and ferroelectric polarization hold potential for application for the development of next-generation nano-memory devices. However, intrinsic 2D multiferroics with a high critical temperature and strong magnetoelectric coupling are still rare to date. Here, we propose a novel mechanism of 2D monolayer multiferroicity. Based on density functional theory (DFT), we predicted that in a Mo2NCl2 monolayer, the non-equilibrium charge disproportionation of Mo ions will induce an out-of-plane electric polarization, making this material a 2D monolayer multiferroic material. More importantly, the magnetic critical temperature is calculated to be ∼168 K, which is larger than those of the recently reported 2D multiferroic and ferromagnetic systems. Our findings also provide a promising platform to control the magnetic properties and electric behavior in 2D multiferroics using an external electric field.