The aim of this paper is to prove the existence of an admissible inertial manifold for mild solutions to infinite delay evolution equation of the form {du/dt + Au = F(t, u(t)), t >= s, u(s)(theta)( =phi(theta), for all theta is an element of(-infinity, 0], s is an element of R,) where A is positive definite and self-adjoint with a discrete spectrum, the Lipschitz coefficient of the nonlinear part F may depend on time and belongs to some admissible function space defined on the whole line. The proof is based on the Lyapunov-Perron equation in combination with admissibility and duality estimates.