We present a functional Schrödinger picture formalism of the (1 + 1)-dimensional O(N) nonlinear sigma model. The energy density has been calculated to two-loop order using the wavefunctional of Gaussian form, and from which the non-perturbative mass gap of the boson fields has been obtained. The functional Schrödinger picture approach combined with the variational technique is shown to describe the characteristics of the ground state of the nonlinear sigma model in a transparent way.