Multivariable plants under input constraints such as actuator saturation are liable to performance deterioration due to problems of control windup and directional change in control action. In this paper, we propose a two-stage internal model control (IMC) antiwindup design which guarantees optimal closed loop performance both at transient and at steady state. The two-stage IMC is based on the solution of two quadratic programs (QP). The first QP addresses the transient behaviour of the system and ensures that the constrained closed-loop response is as close as possible to the unconstrained closed-loop response. The second QP guarantees optimal steady-state behaviour of the system. Simulated examples show that the two-stage IMC has superior performance when compared to other existing optimization-based antiwindup methods. We consider a scenario where the proposed two-stage IMC competes favourably with a long prediction horizon model predictive control (MPC).