We have constructed an exact and stable algorithm for few‐electron systems, with which we have determined the energies of an excited state of the He atom and of the ground state of the Li atom. Significant features of the new method include the following: There are equal populations of random walkers that carry positive and negative weights. The positions of walkers are selected from a distribution that couples all walkers using a Green’s function with a known form. The correct importance functions that take into account the global interactions of the populations are different for positive and negative walkers. This symmetry breaking is an essential element for long‐term stability. A novel transformation of the potential energy facilitates the exact evaluation of the energyE.